Thirteen Days of Midnight by Hunt, Leo

When Luke Manchett’s estranged father dies unexpectedly, he leaves his son a dark inheritance: his Host, a collection of eight restless spirits who want revenge for their long enslavement. Halloween is fast approaching, and Luke knows his Host is planning something far more trick than treat. Armed with only his father’s indecipherable notes, a locked copy of The Book of Eight, and help from school outcast Elza Moss, Luke has just thirteen days to uncover the closely guarded secrets of black magic and to send his unquiet spirits to their eternal rest—or join their ghostly ranks himself.