Time of the Thief by Ivy Hollins

A highway robber. A time traveler with a secret. And a mysterious object that could change everything... Mary makes a living as Scotland's finest highwaywoman, but her life of crime isn't her only secret. She's ready to take on time itself, if that's the only way to get what she wants... Finn has kept a low profile in eighteenth-century Scotland as he tries to hide his double life. He needs Mary's help - but he still can't tell her the truth. It's unfortunate that she already hates him. These two enemies will need to work together if they have any hope of defeating Professor Edmondson's time travel gang. Nothing is as it seems, though - and soon, they will have nothing to rely on but each other... An enemies-to-lovers time travel romance. Book 6 of the Stones of Scotland series.