Searching for Celia

Dayle Salvesen, a bestselling spy novelist from Wisconsin, arrives in London for a writers' conference only to be told that her best friend and former lover, Celia Frost, has died under mysterious circumstances. Or has she? There's no sign of Celia's body, and Celia's flat contains items suggesting she planned to travel.
Dayle joins forces with Celia's ex-girlfriend, Nigerian-British university lecturer Edwina Adebayo, to investigate. Hampering their efforts is Detective Constable Andrea Callaway, who claims that Celia, who ran a refugee center, profited financially from her work rescuing trafficked sex slaves. The deeper Dayle and Edwina dig, the more Dayle questions not only how well she knew Celia, but also how well she knows herself.