You decide that fooling Voldemort is the most important consideration; so you make Peter Pettigrew the Potters' Secret Keeper.  As it turns out, Peter's moral weakness is even worse that you had suspected.  A year ago his fear drove him into serving Voldemort as a spy on the Order of the Phoenix, and now he has new information to pass on to his master: the location of the Potter family.

  Voldemort needed this information because he learned from another Death Eater, Severus Snape, the part of Trelawney's prophecy that Snape was able to hear before being expelled from the Hog's Head: Harry Potter is one of two boys who may have the power to defeat him.  When Snape discovers that Voldemort intends to kill Harry, he begs Voldemort to spare Harry's mother Lily, whom he still loves despite her having thrown him over for James Potter.

  Voldemort barges into the Potters' hideaway, kills James Potter and then goes after Harry.  Lily responds by shielding one-year-old Harry with her body.  Remembering Snape's request, he doesn't kill Lily right away; instead he orders her to stand aside, which she refuses to do.  All he had to do is cast the Stunning Jinx on her and drag her off Harry and he could have had both Harry's hide and Snape's continued loyalty, but he lets his rage get the better of him.  He kills her, then casts the Killing Curse on Harry.  But Lily's sacrifice has given Harry magical protection: the spell bounces off Harry, leaving him with a scar that links their souls, and hits Voldemort instead.

  Voldemort has long been prepared for such a contingency.  He has created a number of Horcruxes - pieces of his soul - so that instead of dying along with his body, Voldemort is turned into a spirit.  To become a person again, he needs one of his Death Eaters to find him, create a rudimentary body for his spirit to inhabit, and then prepare a potion in which to immerse him.  But since he doesn't trust his Death Eaters, the only one who knows how to find him is Peter.  Peter entered Voldemort's service out of fear, and now that Voldemort has become less powerful than his enemies, Peter decides to go into hiding.  He fakes his own death, frames Sirius Black for his "murder" as well as the Potters' betrayal, and then turns himself into a rat and becomes the pet of the Weasley family.  Sirius Black is sent to Azkaban without a trial.  And Snape is so furious with Voldemort for having killed Lily that he joins the Order of the Phoenix as a spy on Voldemort.

  Turn to Chapter 20.