A Deviation From the Course

Harry does have some manners - despite the Dursleys - and therefore thanks Professor Snape for saving his life in 1st Year after Harry learns it was Quirrell trying to kill him all along.
An off-hand comment about Harry living with his Aunt Petunia catches Severus' attention and when Severus investigates, he discovers the snotty little prat he's been given updates on throughout the years doesn't exist.
Severus promptly removes Potter from such a horrible environment but when he takes Potter to Family Services, things don't go as planned. Severus knows how to roll with the punches, however, and this time, he's determined that he won't let Lilly down.