So much happened in Daredevil's sophomore season — Matt Murdock's reignited romance with Elektra Natchios, Wilson Fisk's reintroduction, whatever was going on with the Hand and that giant hole in the ground — so some details might be forgotten over a year later. How did Frank Castle fake his death? The Punisher picks up right where Daredevil Season 2 left off, trusting fans to be able to remember key plot points about its titular antihero's development. But just in case you're fuzzy on the exact twists and turns of Frank's bloody and tragic story, I'm here to help catch you up.
Jon Bernthal's debut as the violent vigilante was undoubtedly the best of the many plot threads in Daredevil's second go-round, so it was pretty much a given that the character would eventually get his own spinoff. When The Punisher Season 1 picks up, most of the world thinks Frank Castle is very much dead. As one character says at the end of the Punisher trailer when his colleague tells him she thinks Frank Castle is back: "The Punisher? He's dead." But there was so much death in Frank's backstory — from his time in the Marines to his own beloved family and the gory trail of justice he left through Manhattan — that it's hard to keep it all straight.
After a season spent tracking down (and mercilessly dispatching) the people responsible for the brutal murders of his wife, daughter, and son, Frank traced the ultimate blame back to a crime lord nicknamed the Blacksmith. When he thought he had located the Blacksmith on a ship docked at the waterfront, Frank arrived to take his ultimate vengeance; but Daredevil arrived as well, to stop his frenemy from taking lives… even if they weren't innocent ones. The Punisher and Daredevil fought, and Frank and the Blacksmith's goons, until the ship's stores of gunpowder were ignited and the entire thing went up in a massive explosion, killing everyone onboard — including (supposedly) Frank Castle himself.
In fact, Frank survived the fiery cataclysm at the docks and was finally able to find the Blacksmith and determine his real identity: Colonel Ray Schoonover, his former commander from his days in the Marines, who had testified on Frank's behalf at his trial earlier in the season. He managed to save Karen from Schoonover's villainous grasp, and dragged the traitor to a cabin in the woods to reap his revenge. Karen begged Frank not to torture the man, saying that he'd be dead to her if he killed Schoonover… but the vigilante responded that it didn't matter, because Frank Castle was already dead.
Ultimately, Frank didn't torture Schoonover, but he did kill him: one shot straight through the head, as Schoonover had taught Frank when he was a young soldier. He then discovered Schoonover's secret stash of military-grade weapons and a bulletproof vest. He took the gear and returned to his family home, where a newspaper article of his own trial — complete with an image of the x-ray of his skull with the bullet lodged inside — inspired him to take a can of spray paint and emblazon the vest with the instantly recognizable symbol of a skull.
He showed up one last time to help Daredevil mop up the Hand ninjas and their evil leader, Nobu Yoshioka. Having achieved his long-awaited closure, Frank burned down his family home and strode away into the darkness, determined to spend his life punishing criminals. Frank had to die so the Punisher could be born.
Given that Karen Page is one of the only people who knows that Frank Castle is actually still alive, and that he didn't die at the docks that day, it makes sense that she would be drawn back into his orbit once he resurfaces during the events of The Punisher Season 1. Now it's time for the rest of the world to learn that Frank Castle is still out there… and still as bloodthirsty as ever.