The New Skin by Mottsnave

The New Skin is a chills-and-thrills vision of the life of survivor Severus Snape, who did not die at the end of Deathly Hallows but was saved by Aberforth Dumbledore and plunged into a desperate struggle to escape from, outwit, and defeat an undead nemesis sent by an unknown adversary bent on Snape's death in a horrible fashion.

The story spans two continents, North and South America, as Snape endeavors to save his own neck and build a new life for himself under a new name, while dealing with all the demons of his past.

No warm fuzzy Snape here, no redemptive romance, just a glimpse into a brilliant mind as we ride along on his danger-filled quest to destroy the undead creature and defeat the enemy who empowered it.

A wonderful cast of supporting characters, and a fascinating exploration of the magical science of potions.  Spine-tingling suspense and laugh-out-loud humor. You will appreciate Snape as never before.