Snape's fourth memory: On the [Hogwarts Express], Snape tries unsuccessfully to console Lily, who is still upset that they made [Petunia] so angry. But, they are interrupted by James Potter and his buddy Sirius, already making fun of Snape, and Snape and Lily leave to find another compartment.
Snape's fifth memory: Harry watches as Snape's [Sorting] takes place. James, Sirius, Lupin, and Pettigrew all land in [Gryffindor], as does Lily, though Snape moans at this. Snape himself, of course, is placed in [Slytherin].
Snape's sixth memory: Snape and Lily argue about Snape's friends, the [Dark Magic] he's getting himself mixed up in, and his spying on James Potter and his friends. When Lily calls James an "arrogant toerag," though, Snape is so happy that he hears virtually none of the other things she says.
Snape's ninth memory: Snape meets [Dumbledore] to request his help in protecting Lily Evans Potter from Voldemort, now that Voldemort has heard part of the [prophecy] and intends to kill the whole [Potter family]. He also vows to do "Anything" in return.
Snape's eleventh memory: Again in [Dumbledore]'s office, Snape complains about Harry's arrogance, though Dumbledore tells him that his other teachers rather like him. He also asks Snape to help him keep an eye on Quirrell.
Snape's twelfth memory: After the Yule Ball, Snape tells [Dumbledore] of his [Dark Mark] growing darker, and of his intentions to stay put (rather than flee like [Karkaroff]) when Voldemort returns. Dumbledore leaves him with a cryptic message: "You know, I sometimes think we Sort too soon...."
Snape's thirteenth memory: Once again in [Dumbledore]'s office, Severus Snape casts charms to confine the terrible curse to Dumbledore's hand, after he put on the [Peverell ring] and was nearly killed. With only a year or so left to live, though, Dumbledore hatches a plan: Snape vows to protect the students of [Hogwarts] when Dumbledore is gone, and agrees to kill Dumbledore when the time arrives.