When British doctor Arlo and his fiancée nurse Jen volunteer in war torn Mosul Iraq, a single act of compassion sets off a chain of violence. Jen is murdered by a sadistic ISIS commander known only as Spider and Arlo, who is trapped in a collapsing city, is forced to make choices that will echo far beyond Mosul - and none of them will leave him whole. Thousands of miles away in England, ex-soldier Steve Foley and his son Eddie, are rebuilding their lives after surviving a terrorist plot. But when chilling threats appear, signed only with the single letter Q, the Foleys are dragged back into a deadly game that blurs the lines between hunter and hunted. In another part of the country, an elderly couple are coerced into smuggling two strangers into the country - a decision that will entangle them in the same web of deceit and vengeance. As their paths converge, they will all discover that the quest for survival and retribution can unleash a destructive darkness. When the past refuses to stay buried, anyone can kill.