Back from the future, Supergirl is ready to keep her impossible promise, despite the horrors of the world she just left. And to bring a miracle to life, she must enlist the aid of the last DCU hero you ever expected to see again — one who's supposed to be dead! As if that clue will help you narrow it down!
As Supergirl and Wonder Woman foil some bank robbers, Kara tells her that she is going to cure cancer. When Wonder Woman asks her what she means, Kara tells her that she promised a kid she'd do it. Diana asks why she promised that to a kid. Kara says because he was dying. Wonder Woman tells Kara to quickly fly back to Themyscira and back to get the purple ray. As soon as she hands it to Diana, she delivers a suckerpunch that sends Kara flying back. Getting a slight bloody nose, Diana uses the ray on Kara.
Diana asks Kara if Superman knows about this and Kara says he was there but had to fly off right away. Diana tells her she wanted her to experience the purple ray so she can see the amazing technology they have, yet even it cannot cure cancer. Kara tells her she gets that things keep happening but she's seen the future and figures instead of saving a few, they could save millions.
A couple months ago in Gotham, some gang members shoot and old guy. After they run off, the man comes back to life. It is the Resurrection Man. He proceeds to leave Gotham and travels around until today.
Supergirl finally locates the Resurrection Man in California. She wants to ask him some questions and he agrees if she'll buy him some bourbon. She tells him her story and he tells her it's the stupidest idea he's ever heard in his fifty thousand years of living. Supergirl thinks it could work. They just need to keep killing him until he develops a power that can cure cancer.
Resurrection Man gets up to leave. Supergirl asks him to wait. Finally he tells her to go ahead and kill him. They go outside to give it a try. Supergirl hesitates for a while and finally decides she can't do it. He tells her it's okay. It's to help save a kid's life. She still can't do it. He tries to make her feel better by saying dying is a natural part of life. She tells him it's not natural for a five year old to have to die.
The two of them fly to a federal penitentiary in Montana and bust out Dr. Luzano. Supergirl tells the camera that she will bring him back and help repair the damamge. She flies off with Luzano and Resurrection Man.
At the Daily Planet, Perry White hands the story of Supergirl's break-in to Kent and Lane, telling them to decide which one will cover it. Clark grabs it and says he'll deal with it.