Fifth book (but second in a new story arc) in the Iron Chronicles series, described by SFF World as 'Neil Gaiman's American Gods meets Jim Butcher's Harry Dresden'.
After twelve years of secret training, Atticus O'Sullivan is finally ready to bind his apprentice, Granuaile, to the earth and double the number of Druids in the world. But on the eve of the ritual, the world that thought he was dead abruptly discovers that he's still alive, and they would much rather he return to the grave.
Having no other choice, Atticus, his trusted Irish wolfhound, Oberon, and Granuaile travel to the base of Mount Olympus, where the Roman god Bacchus is anxious to take his sworn revenge - but he'll have to get in line behind an ancient vampire, a band of dark elves, and an old god of mischief, who all seem to have KILL THE DRUID! at the top of their to-do lists.