Always Practice Safe Hex (Stay A Spell, Bk. 4)

Everybody likes Livvy Savoie. Not only does she have the magical gift of persuasion, perfect for working in PR, but her natural charisma also charms everyone she meets . . . except Gareth Blackwater, the annoyingly brilliant work nemesis who seems to despise her. The feeling is mutual.
 
A grim reaper, Gareth is rarely, if ever, moved beyond his broody, stoic state. But when he’s partnered up with Livvy in a company competition for charity, his peace of mind is destroyed. He’s convinced the flesh-melting attraction he feels must be her witchy magic at work.
 
Now forced to collaborate, their constant bickering turns into sparks flying, and Livvy learns that this enigmatic grim is more powerful than any supernatural she’s met. And when Livvy becomes the obsessive target of a dangerous warlock, the full force of Gareth’s abilities becomes shockingly apparent. Because no one is going to hurt his Livvy . . .