Obviously, by the title, prison inmate Eduard Delacroix is electrocuted in this book. Unfortunately, it's at the hand of Percy Wetmore, the prison guard who's been bullying Eduard from the beginning. He's the one who sabotages the execution, giving Eduard a painfully long-drawn-out death. This scene is rather gruesome and will remind readers that this is still Stephen King writing, even though The Green Mile isn't King's usual horror fare.
While Eduard dies, though, Mr. Jingles is "resurrected" by John Coffey, after Percy had stepped on him in the previous book, "Coffey's Hands." Like the sudden endings in most of these books, this one has another good cliffhanger, in regards to Coffey's innocence. These sudden endings can be aggravating, but they were a very good marketing technique at the time of publishing--to keep the loyal reader addicted for the next installment, especially for the following two: "Night Journey" (#5) and "Coffey on the Mile" (#6). However, since the complete serial novel has since been published, I'd recommend getting that one instead.