Second half of my story "Regrets". Severus Snape thinks about/remembers Remus Lupin.
Remus Lupin has just arrived at Hogwarts to teach DADA. He thinks about/remembers Severus Snape.
What if You-know-who finds out that one of his Death Eaters is a spy? Takes place at the beginning of Harry's 5th year at Hogwarts