Chapter 4: Snaps and the Second Week is the chapter following Chapter 3: To Start A Year.
The chapter begins with James Potter and Remus Lupin nearly getting into a fight with Nicolai Mulciber, which Donna Shacklebolt attempts to break up. The Auror, Jack Lathe intervenes and asks to interview James about Carlotta Meloni's attempted suicide.
Marlene Price visits Adam McKinnon in the hospital wing and it is revealed that the attempted suicides were the results of accidental exposure to darkly magical objects.
Lily Evans is studying in the library when she is interrupted by Alice Griffiths, who is worried about her boyfriend, Frank Longbottom. Alice tells Lily about her problems with Frank, and Lily begins to suspect Frank of cheating, but she lies to Alice, telling her it was probably nothing and promising to ask Frank about it. After Alice leaves, Severus Snape arrives and again asks to repair their friendship, but Lily refuses. After Severus gives up, Lily is interrupted a third time, this time by James Potter who teases her, and departs, cryptically calling her "Snaps", a nickname that confuses Lily.
James and Sirius prank Kevin Sherbatsky by vanishing his hair twice, earning Sirius a detention. Afterwards, Sirius vaguely asks about James's father, leaving the reader in the dark about James's relationship with Alex Potter.
That evening, Frank supervises Lily's detention wherein she asks about Alice, but Frank dodges the questions.
Lathe interviews Lily who tells him that Carlotta Meloni is a vegetarian, a fact that interests Lathe. After answering a few questions about Adam, Lily leaves Lathe still puzzling over the suicides.
James runs into Adam in the Gryffindor common room, learning that Marlene stood him up to be with her boyfriend, Miles Stimpson. James then runs into Lily and they banter back and forth, at the end of which Lily discovers the source of her new nickname; "Gingersnaps." James congratulates her, but doesn't reveal the true meaning of the nickname.
- This chapter introduces Jack Lathe and Miles Stimpson.
- This chapter starts the sub-plots of Donna and Lathe's relationship, Frank and Alice's relationship, and James and his father's relationship.