Straight after school in 1979, Severus Snape becomes a death eater. He fell in love with the dark arts and fell into the wrong friend group at school. Snape starts snooping at Hogwarts for the death eaters in 1980. He overhears the first part of the prophecy when he listens in on an interview between Sybil Trelawney and Albus Dumbledore. After Snape tells Voldemort what he heard in early fall of that year. In August 1980 Snape learned that Voldemort had decided to kill the potters. He asks Voldemort to spare Lily Potter. Snape becomes desperate and tells Dumbledore of Voldemort’s plans. He begs Dumbledore to keep Lily safe in return for his loyalty. He casts the fidelius charm in the potters house but it breaks when Peter Pettigrew betrays the potters to Voldemort. In November, Snape is distraught over Lily’s death as he was in love with her. He gives his allegiance to Dumbledore but he tells him not to tell anyone of his love for Lily. In early winter, Karkaroff announces Snape as a death eater and Dumbledore vouches for his loyalty.