Sienna Cole doesn't lose. Not clients, not arguments, and certainly not to Xavier Hart — the agency's least favorite outside consultant, a man who's made it his personal mission to tell anyone who'll listen that matchmaking is a scam for people too scared to be alone.

Unfortunately, Xavier is also the brother of the agency's newest golden-couple success story, which makes him impossible to avoid at every engagement party, every press mention, and — worse — every meeting about how to fix the reputational mess a rival firm just dropped on their doorstep.

The fix: a high-profile charity gala, co-hosted, co-branded, and co-run by the two people in the building who agree on absolutely nothing. Sienna wants it perfect. Xavier wants it over. Neither of them wants to admit how much they're starting to want the other one in the room.

Late nights spent arguing over seating charts and vendor contracts have a way of wearing down the armor. Sienna's cutthroat reputation turns out to be built on a heartbreak she's never let anyone see. Xavier's contempt for love turns out to be built on the exact same thing. What starts as enemies forced to share an office becomes something neither of them has rules for.

When a corporate buyout threatens everything Sienna's built, Xavier has one chance to prove that some things are worth more than being right.

*The Rival's Rules* is the second standalone-but-connected novel in the Hearts, Inc. series — a sensual enemies-to-lovers workplace romance about two people who mistake being guarded for being safe.