This drama has four timelines,determined by four numbered mailboxes.Mailbox 01 doesn't appear in the show, it is Where the old man & his cart and The Cat originally belongs to.That old man who appeared across all timelines with his cart is probably some kind of deity who repays kindness and Changes people's fate according to it.

The cat is the 'messenger' here (To deliver the Letters) and it can also travel across all timelines as we see.Mailboxes are just 'portals' that the cat uses to Jump from one timeline to another. It gets activated at 12 on Midnight, and the cat messenger jumps from one timeline to another Through it,bringing the letters to destined places.As the cat is a time traveller,it can foresee what's happening & what's gonna happen,we see in ep 12 that the cat prevents A'xun from leaving early and delays him to return to collect the letter at the end.


Mailbox 02 demonstrate 2nd Timeline which is 1991.Mailbox 03 represents 3rd timeline Which is 2026.


Mailbox 04 appears at the very end of the drama,with their changed fate/Altered future of 2026,where shen cheng received the final letter of A'xun & A'Tang. Yes,he didn’t disappear (look at the Watch in his hand, It's the same watch shen cheng has been wearing the entire time).His presence in the changed timeline also confirms that Shen Cheng wasn’t Ye Hai Tang's biological son.As for how he became Atang's son,or who is shen cheng's dad, Drama didn’t mention it, leaving the audience to speculate.


When Yu Nian awakens at the end, it's Timeline 04.Yu Nian no longer has her father, As A'xun wasn't imprisoned, he didn't get to know Yu Nian's father. Her consciousness traveled directly to timeline 04 From Timeline 03, so she has all the memories of Timeline 03 with newly created memories of her current Timeline 04.


As for Tang Yi Xun & Ye Hai Tang,They had Their deserved happy ending in the altered timeline.Post credit scene polaroids show their little moments of journey from 1991 to 2026.Translations of the polaroids:

''Goodbye Mei Wan. Signed, Tang Yi Xun,Ye Hai Tang''
'Watching my first snowfall with A'Xun'
'A'Xun, Happy 20th Birthday 1992'
'A'Xun, Happy 30th Birthday 2002'
'A'Xun, Happy 40th Birthday 2012'
'A'Xun, Happy 50th Birthday 2022'
'A'Xun, Happy 54th Birthday 2026'


Now, Answers to some questions.

1.Who is shen cheng's dad and Ye Haitang's husband?  Many people think shen cheng was the child of Shen Xiaojun & another woman (most likely Wang Manyu), and A'tang may have raised the child after their biological mother passed away.But I do not believe shen xiaojun is shen cheng's dad at all, bcz shen is a common surname,& A'tang could've met shen cheng's dad later in her life,also she left Meiwan Town not long after A'xun's conviction & attended Nanjiang Normal University in another city, married many years later than their high school days,It didn’t look like she was still in contact with all those people From Meiwan Town back in the days. plus,if shen xiaojun was his father,Don't you guys think It's weird that shen cheng didn’t know anything about his parents' high school life or days in Meiwan town,he didn’t even know about a place Named Meiwan town,only knew the new name of that place 'Pushui'

Most possibly, she married someone with shen surname but adopted an orphan as their child (from the welfare house of kids she was volunteering in for years) This is also the very reason that even shen cheng didn’t know until the end that he wasn’t his parents' biological son (he said to yu nian that he probably won't exist in changed future as his father won't have him)


2.Some said, is there a possibility shen cheng was A'xun's son but he didn’t know?NO HE IS NOT.shen cheng was born in 1999,Yu Nian was born is 2002.A'xun went to prison in 1992 February & served 13 years,got released in 2005,called A'tang,but call received by her son shen cheng (who was 6 years old at that time),later he went to yu zhi hong's house in Bixian city and lived there as yu nian's dad.

Thanks for this😍

Thankyou for this detailed explanation it cleared many of my doubts but I've a doubt, did the A'Xun in 2026 in the start of the drama how did he knew about the Mail box thingy as he sent the Love Letter which started it all, was this happening in a loop?? Did 2026 A'Xun knew that theMail Box will deliver the message to A'Tang in 1991.


2026 A'xun had Alzheimer's. In Ep 6 very beginning scene, we see him in his neighborhood in Beixing city encountering that deity/old man & his cart,helping him to move.The cart had that Mailbox 03. Then the Mailbox appeared in that neighbourhood near the place Where Older A'xun lived. In ep 1 we see the security Guard saying It's been 2 months that Older A'xun has been sitting around there from time to time (Very likely behaviour for a person with Alzheimer's bcz they tend to get confused about time & place so they often do repetitive things, we also see Old A'xun asking the security Guard 'what date is today' in that scene)

As for why would he particularly sit there near the Mailbox, that's obviously related to his mental condition. Patients with Alzheimer's,they have their conscious moments and confused moments. when dementia phase is triggered, they often become childs with only childhood memories remaining, and sometimes young adults with only young adulthood memories intact, and they behave according to that.A'xun belonged to 90s generation, The Mailbox must be something he felt connected to in his confused moments, in addition, he had his regrets and unfulfilled wishes of being with A'Tang for 35 years,in his mental condition, He probably felt immense regret & sadness. when security Guard asked him why he sits there,Old A'xun says he's waiting for letters, but when yu nian asked ''who'll write you a letter?" he replies, "I'm not waiting, I'm sending Letters" So he's basically sick & confused and neither he was writing letters or sending them .The only one he sent was the "love letter" which started all this.

Now comes the love letter part. How did he end up writing that? It was actually his "final words" or "Dying words" that had no audience to share to (just like ye haitang's first letter where she potentially wrote a suicide letter before going to stab ye yibo,and had no one to give it to,so she put it in the mailbox)... The Note Old A'xun left for yu nian says "i no longer want to be your burden,i Won't leave with you to Beijing... this illness is not very bad for me" (bcz it keeps him in a state Where he's remembering those good times of 1991?)...Old A'xun put the ''love letter" aka his final words of his lifelong regret in the mailbox and went to the cemetery and lived there for days until police found him.So he practically was ill to that point he went to his grave awaiting his own death,& just in case seeing A'tang for the very last time.


So i don't think he recognized the mailbox or he knew his letter would reach 1991, so it wasn’t happening in a loop,from my understanding.

Shen Cheng is THEIR biological son

You can guess it early on in the drama 

She has no husband  - is a single mother - and keeps visiting his tomb - 

meaning she either lied about her husband … (or if she actually married, she was already pregnant or with child  and her husband only gave Shen Chang  is name… explaining why they split without keeping contact later on…)

He has been Their biological son all along…

Probably conceived during their short blissful time when they lived together 

That’s why is why he doesn’t disappear in the end

- they gave a hint in ep 11, when she doesn’t want him to deliver the last letter, 

because it will most certainly alter the past, and she fears Shen Cheng will never be conceived- by his mother, 

because at that point, none has understood that he is their biological son, and has already been conceived no matter what/will be conceived no matter what

OP The only reason why he doesn’t disappear when they alter the past for the better…

That’s why he smiles at the end

He has understood it .

Logical and brilliant in my opinion :)

*****

And why she doesn’t disappear obviously

Because she was his adopted daughter and never biologically related to them…

She gets rewarded in the end for her good deeds 

Getting a better life - but with a different family, and no longer her adopted “father”

You are actually having a very wrong idea.i have already answered this,you probably didn’t read the whole thing. Shen cheng was living in England with his dad since he was 10 years old.his parents divorced when they moved to England bcz she didn't want to leave. 

"Muito obrigada pela explicação. Me ajudou muito. Parabéns pela escrita, excelente discernimento. Adorei!"

I think Shen Cheng is Shen Xiaojun's son, but not A'Tang's. I want to think that because that way he doesn't have to disappear. But I also found what he said about himself interesting. He used to be a chubby kid and has always liked sugary things. I know that might not indicate anything, but I see it as a small clue because Shen Xiaojun's father was the owner of the sugar factory, right? Whatever the case, I hope Shen Cheng is still alive in another timeline.

Fenghua sugar factory was where A'tang's parents worked at...& shen Dashen (father of shen xiaojun) tried to steal money from there once, got caught but A'tang's Mom saved him telling the security that he was her cousin...Shen Dashen said ''later i founded my own company" but it wasn’t mentioned what kind of company he owned...shen xiaojun said his father owns a nightclub (while talking to A'xun) & because of some happenings in the nightclub, Bao gang hold a grudge Against shen Dashen & kidnapped shen xiaojun to get money from his father.

Anyways, they deliberately didn’t reveal who's his father & also deliberately implied in the last scene that Shen cheng is alive in the changed timeline...

 Salwa Nice:

Fenghua sugar factory was where A'tang's parents worked at...& shen Dashen (father of shen xiaojun) tried to steal money from there once, got caught but A'tang's Mom saved him telling the security that he was her cousin...Shen Dashen said ''later i founded my own company" but it wasn’t mentioned what kind of company he owned...shen xiaojun said his father owns a nightclub (while talking to A'xun) & because of some happenings in the nightclub, Bao gang hold a grudge Against shen Dashen & kidnapped shen xiaojun to get money from his father.

Anyways, they deliberately didn’t reveal who's his father & also deliberately implied in the last scene that Shen cheng is alive in the changed timeline...

Ok, you are right, I don't know why I thought his father was the director or the sugar factory. So the things he told about his childhood give no clues about his father.

@salwa nice: I don't think 2026 A'Xun wrote a dying message and didn't have an audience so he dropped the letter in the mail box and went to the cemetery. The watch man said " He started showing up like 2 months prior to his disappearance and was waiting for something. He disappeared infront of the watchman". Old A'Xun wrote that letter when his daughter gave a ultimatum about moving the very next morning. He also kept saying about the redevelopment that they cannot take away the mailbox so not sure how the old A'Xun knew that the mailbox was the portal.

 Pearl Harbor:

@salwa nice: I don't think 2026 A'Xun wrote a dying message and didn't have an audience so he dropped the letter in the mail box and went to the cemetery. The watch man said " He started showing up like 2 months prior to his disappearance and was waiting for something. He disappeared infront of the watchman". Old A'Xun wrote that letter when his daughter gave a ultimatum about moving the very next morning. He also kept saying about the redevelopment that they cannot take away the mailbox so not sure how the old A'Xun knew that the mailbox was the portal.

The Watchman said old A'xun sat there frequently for 2 months waiting for something,he even asked Old A'xun what he's waiting for (ep1)..and He replied ''I'm waiting for a letter" but on the same episode, when yu nian asked his father ''who'll write you a letter?" he replied, "I'm not waiting, I'm sending Letters".... i think he was just confused in his mental condition whenever his illness triggered...about the anchor mark page he wrote the letter,i don’t find it very unlikely that he had that old paper (he had stored a bunch of tickets and other old stuffs with him after all these years,keeping that anchor mark paper From the bookstore haitang worked at didn’t feel much strange to me).. ..Also,if he knew the mailbox was the portal,why'd he wait for 2 months without immediately sending letters to 1991 by Himself and assuring he didn't do the mistake of killing? 


Do you think he really 'disappeared' in front of Watchman? i think the Watchman was too occupied looking inside the mailbox that he didn’t notice him leaving,but as the watchman saw the Letter got disappeared, he was scared and thought old axun gone missing in the air as well 😅... bcz his disappearance doesn’t make much sense as later the police said he was in the cemetery for some days until they found him. And he also didn’t appear in any other timelines to prove that he time travelled, unless he became the cat,or his consciousness travelled through the cat. 


Suppose,he knew about the mailbox, the biggest question is how? The Mailbox first appeared in 1991 with Old A'xun's letter, so It's likely that OG timeline of 1991 didn’t have a mailbox to begin with...even the logic of time loop happening Isn't compatible here,bcz sequences of events Don't match. I don’t think writers intended to write it in a very complicated way, i find the screenwriter handling the 'time travel element' slightly in a ''lovely runner" way, idk if you watched that drama or not.(though the fl physically time travelled there,& here only the letters travelled) 

I have a question, what "twelve letters" do the title Twelve Letters refer to?

In total it was 12 letters in the drama...& episode numbers are 12 also,so i guess thus the Title was decided to be like this

 Haveninmuse:

I have a question, what "twelve letters" do the title Twelve Letters refer to?

1️⃣ **EP01 Love Letter**|A Xun — Year 2026
2️⃣ **EP02 Will/Testament/Suicide note**|Ye Haitang — September 3, 1991
3️⃣ **EP05 Hello, Stranger**|Ye Haitang — September 12, 1991
4️⃣ **EP05 Time-Space Communication**|Yu Nian — November 12, 2026
5️⃣ **EP06 Dragon Sucking Water**|Ye Haitang — September 23, 1991
6️⃣ **EP07 Azai, let’s eat the Fish Cake**|Shen Cheng — 2026, Ye Haitang — 1991
7️⃣ **EP08 Prison Letter Sent**|Tang Yixun — 1992
8️⃣ **EP08 Prison Reply Letter**|A Tang — November 9, 1992
9️⃣ **EP09 Stay Away from Tang Yixun**|Shen Cheng — November 17, 2026
🔟 **EP11 He Won’t Hurt Me (Is He Good to Your Mom?)**|Ye Haitang — November 24, 1991 (Tang Yixun)
1️⃣1️⃣ **EP12 Don’t Go to the Hillside, Don’t Kill**|Yu Nian & Shen Cheng — 2026
1️⃣2️⃣ **EP12 The Final Letter**|Tang Yixun & Ye Haitang 1992


credit - @bananabanana