Lord Loss: Vein appeared during the massacre of Grubbs family, and fought Grubbs while Dervish was playing chess against Lord Loss. After disobeying Lord Loss's orders, Vein is killed.
Demon Thief: Vein accompanies Lord Loss in his castle near the end of the book.
Bec: Vein appeared at Lord Loss' side near the middle of the book where the idle boy, Bran is (much to Lord Loss' annoyance) playing with her, and stops Bec from leaving the tunnel at the end of the book.
Vein is Lord Loss' favourite familiar in Bec, where she accompanys him throughout most of the book. She can not be that important to Lord Loss, however, as she is apparently destroyed by Lord Loss for disobeying him at the end of the first book, Lord Loss. She does, however, re-appear in novels after Lord Loss has killed her, but this is because the novels are set in a time period before Grubbs' and Dervish's battle with Lord Loss. She seems to be replaced with a new demon, Gregor - a cockaroach-like demon, who is later killed as well.