Book 4 of the Roma Nova series, the alternate history thrillers by Alison Morton.

Late 1960s Roma Nova, the last Roman colony that has survived into the 20th centuryAurelia Mitela is alone - her partner gone, her child sickly and her mother dead - and forced to give up her beloved career as a Praetorian officer. But her country needs her unique skills. Somebody is smuggling silver - Roma Nova's lifeblood - on an industrial scale. Sent to Berlin to investigate, she encounters the mysterious and attractive Miklos who knows too much and Caius Tellus, a Roma Novan she has despised and feared since childhood.Barely escaping a trap set by a gang boss intent on terminating her, she discovers that her old enemy is at the heart of all her troubles and pursues him back home to Roma Nova...