Romancing His Rival by Jennifer Shirk

Hopeless romantic Elena Mason doesn’t often hate people, but she hates her ex-fiancé’s insufferable best man, Lucas Albright III. She just knows Lucas is the one who talked her ex out of getting married—so Lucas is clearly the cause of all her problems.

And now she’s expected to work with him? Oh, heck no.
Lucas Albright wants nothing more than to make partner at his advertising firm, and he knows he works best alone. But then Elena ends up as his partner on an account that could win him a promotion. He had a great reason to end her engagement, not that she’d ever believe him. Still, he’s willing to try working as a team.

Unfortunately, his new “partner” wants him dead.
Elena knows she’s going to have to give in and work with her nemesis, though nobody said it had to be easy for him. But what happens when fighting starts feeling a whole lot like falling in love?