Masked Promises by Diana Bold

When Lucien Strathmore, the Earl of Hawkesmere, sets out to find his abducted little sister, he finds the woman he’d once loved instead. Serenity Pratt had been the gamekeeper’s daughter, and they’d spent one magical summer together, but then she’d disappeared without a trace. Now, she’s back in his life and he must deal with the tragedy she’s been hiding.

In order to solve the mystery that tore them apart, he must take up the mask of Prometheus, the masked avenger he and his brothers created to deal with their troubled childhood. But what he finds forces him to make an untenable decision.