Undercover Honeymoon by Jo Watson

When Private Investigator Lizzy Brown is hired to follow a cheating spouse, the last person she expects to run into is Cameron Anderson: the man she dated for a grand total of 6 hours, and the real reason she left the Police Academy all those years ago. Something Lizzy definitely isn’t still bitter about.
Cam, tasked with a money-laundering case, never thought he’d find himself once again squaring off with Lizzy – and most certainly not in a romantic and glamorous Seychelles resort. But when their separate cover stories are put at risk, the pair are soon forced to masquerade as a honeymooning couple to cover their tracks.
Faking a marriage with your ex is bad enough, but when Lizzy and Cam find themselves tangled in a criminal conspiracy bigger than their bitterness, they realise that their relationship lie might be the only thing keeping them alive.

But as old feelings resurface, are they really just playing the part?