"Because you seem like the sort who can't let things go. The sort who couldn't possibly let a vulnerable young girl get taken again. So you must have her under your very handsome, protective gaze."

After learning about Martha's secret son and quitting the agency, Tom's content chopping firewood in Avebury and counting the minutes until Isabella comes home.

But when two young women show up in London in the middle of the night demanding to speak to Tom, he's unwillingly dragged back into the seedy world of human trafficking.

To find a third woman, the key witness in Operation Sweetpea and the only person with the knowledge to bring the trafficking ring down, Tom works to decipher clues left by the murdered MI5 agent charged with her protection.

With foes attacking from every direction and allies deceiving him, Tom must figure out who he can trust before Operation Sweetpea implodes and he's left with more deaths on his conscience.