A Turn of the Tide by Kelley Armstrong

In Thorne Manor there is one locked door. Behind it lies a portal to the twenty-first century, and nothing is going to stop Miranda Hastings from stepping through. After all, she is a Victorian writer of risqué pirate adventures—traveling to the future would be the greatest adventure of them all.
When Miranda goes through, though, she lands in Georgian England…and in the path of Nicolas Dupuis, a privateer accused of piracy. Sheltered by locals, Nico is repaying their kindness by being their “pirate Robin Hood,” stealing from a corrupt lord and fencing smuggled goods on the village’s behalf.
Miranda embraces Nico’s cause, only to discover there’s more to it than he realizes. Miranda has the second sight, and there are ghosts at play here. The recently deceased former lord is desperate to stop his son from destroying his beloved village. Then there’s the ghost of Nico’s cabin boy, who he thought safe in a neighboring city. Miranda and Nico must solve the mystery of the boy’s death while keeping one step ahead of the hangman.

It may not be the escapade Miranda imagined, but it is about to be the adventure of a lifetime.