Set on a sleeper train traveling from Glasgow to London, a government agency desperately tries to intervene in the rapidly-escalating events onboard. Can two people who’ve never met, one on the train and one not, work together to save the lives of its disparate group of passengers as the Heart of Britain service hurtles towards what might quite literally be its final destination?

One victim, found dead on a London street. Four detectives, in four different time periods, must solve the mystery to protect Britain's future.