Sam has actue lymphoblastic leukemia, for the third time. He's not going to survive it, so he does what anyone who wants to be remembered would do: writes a book. His book is a memoir, full of lists, like the list of things to do before he dies that his friend Felix, who's also pretty ill, suggested he make.
There's not much to be said about the plot, because we know at the beginning how it's going to end. This is not a book wherein someone creates a cure for cancer. It's sad, but it's sweet, and wonderful, and terrible.