Beauty and the Thief. The Royal Saboteurs, #1

Callahan Kelly is a conman, pure and simple. With his dark hair, dark eyes, and dimpled smile, he can smooth talk anyone out of anything and has a keen nose for sniffing out liars and thieves. So clearly someone somewhere made a mistake including him on a train heading toward a training ground with an elite group of agents for the Crown. But Baron, the leader of the newly formed Royal Saboteurs, makes a deal with Callahan: stay until his troubles in London die down, and if he still wants to go, he'll be paid and discharged.
But Cal finds the training at the camp fascinating, and even more intriguing is Bridget, the red-haired beauty who's immune to his charm. When Cal is asked to partner with Bridget to infiltrate a group of Irish separatists or return to London, the choice is neither simple nor easy. Bridget Murray was sent from London to serve as Baron's secretary. She never expected to be given the chance to carry out a mission for the Royal Saboteurs.
She doesn't like Callahan Kelly from the moment she meets him. But when they're paired for to infiltrate the Irish nationalists, she reluctantly agrees to pose as his wife. Living in close quarters with Callahan isn't as awful as she expected, and that's just the problem. The closer they become and the more real the danger surrounding him, the more she realizes she doesn't ever want to let him go.