Dead Money (Jack of Spades #5‪)‬

Barton Montoire's fragile hold on his emotions is worn thin by exorcisms and fear. Even though he's beginning to realize the full potential of his abilities as a ghost, he has no power to stop his lover's plot to end the darkness that has threatened their relationship for close to a year, not with all their friends in the line of fire.
In all of time, there have existed few men who transcend the bonds of life and death, who see the spirits as clearly as the living. These men possess the ability to summon others, creating doorways between realms, physical and metaphysical. A dusty tome written in cryptic language reveals terrifying secrets, but with a little help from his friends, Sabine Brusilov knows what must be done. For the good of humanity and supes alike, he must call forth the shadowy demon, leading it into a trap.
Unfortunately, talent is not skill, and the ability to summon cannot be mastered by taking a class or two and scouring the internet for information. With Bart at his side and his friends at his back, Sabine brings talent, skill, and strength of will to battle evil before it can join the gathering forces of darkness that menace New Orleans.
With dead money on the table, is love enough to take the hand?