Episode Summary
Ye Haitang's letter disappears, and she tries to contact Tang Yixun, who is in deep trouble with a local gang. Her abusive father, Ye Yibo, beats her to get the house deed. After Tang Yixun confronts her father, he and Haitang team up to investigate the mysterious letterbox where her letter went missing. They discover it might be a channel for communication across time when a new letter appears out of nowhere, seemingly connected to a calico cat and events in the future.

Spoiler Alert
"Twelve Letters" Episode 4: Bad Dads and Magical Mailboxes
A Really Bad Day
You think you're having a bad day? You're probably not having a "getting beat up by two different people" kind of day.
Tang Yixun's Problems
The episode kicks off with Ye Haitang trying to call Tang Yixun.She's worried because a letter she wrote has vanished. But Tang Yixun can't answer. He's busy getting cornered by a gang leader named Bao Ge. One of the thugs gets annoyed by the ringing phone and smashes it. Things get serious when Bao Ge tells Tang Yixun and his friend Li Chadong that he wants a leg from each of them as payment. To save Tang Yixun, Li Chadong promises the gangster 10,000 yuan. As if that wasn't enough, some other thugs decide to get their own revenge by trashing Tang Yixun's billiard hall.
Haitang's Dad Problem
Haitang's dad, Ye Yibo, is truly something else. He sees Haitang calling Tang Yixun and drags her home. He forces her to kneel in front of her late grandmother's portrait and starts a whole dramatic scene about being in debt. He wants to sell the house. Haitang refuses. So he beats her until she gives him the property deed.
Picking Up the Pieces
After all that chaos, we get a quiet moment between our two leads. It doesn't last long, though.
A Moment of Tenderness
Haitang is upset after her father's attack and finds comfort in a picture of her grandmother. Later, she goes to find Tang Yixun and sees blood on his door. She's worried. He shows up, trying to pretend he's fine, but she sees his injuries. She doesn't push for details. Instead, she just quietly helps him with his wounds. While she's tending to him, he notices the fresh bruises on her wrist and knows exactly who did it.
Tang Yixun Pays a Visit
Tang Yixun is not about to let that slide. He finds Ye Yibo at his gambling spot. He puts on a tough act, pretending to be a debt collector. Ye Yibo, who was acting all high and mighty a second ago, immediately gets scared. Tang Yixun warns him to never touch Haitang again. Right after Tang Yixun leaves, Bao Ge's men show up to talk to Ye Yibo. You can see where this is going.
The Mailbox Mystery
The next day, it's raining. Tang Yixun brings Haitang some buns, and she finally tells him why she called. Her letter is gone.
The Stakeout
Haitang mentions she also found a love letter addressed to her, which makes her think something is off with the letterbox.So, they decide to investigate. Tang Yixun has her put an empty envelope in the box, and they hide nearby to see if anyone takes it. They wait all night. Nothing happens. At some point, Haitang falls asleep on his shoulder, and he just lets her sleep. They decide to go home and check on the letter in the morning. For the next three days, the envelope just sits there.
A Magical Cat Appears
This is where things get weird. The show jumps to a different time, where a woman named Yu Nian is with Haitang's son at the same letterbox. A security guard tries to explain something to the boy, but it sounds too strange to be believed. Then, a calico cat appears. The guard tosses a letter into the box.
The show snaps back to 1991. Haitang and Tang Yixun are about to give up on their stakeout. Then they hear a meow. The same calico cat is sitting by the letterbox. On a hunch, they open the box again. Their empty envelope is still there. But now, there's a new letter inside.