Wayward Devils by Devon Monk

Cursed to follow Route 66 for nearly a hundred years, Brogan and Lula Gauge have made a deal with Cupid to find the spellbook of the gods—a book powerful enough to destroy the world.

But they aren’t the only ones looking for it.
The evil goddess, Atë, has already tried to kill them once for the book, and now Brogan and Lula must race to find it before Atë finds them and finishes the job.
Luckily, a coven of honky tonk witches in Shamrock, Texas claims to know where the book is hidden. But their information comes at a great price. Brogan and Lula must help the witches kill an ancient monster. To do so, they will have to form an alliance with an old enemy who wants the Gauges dead.

Brogan and Lula’s luck is turning, but whether it’s good or bad teeters on a knife’s edge: trust the devils they know, or go all in with the wayward devils they’ve just met.