The Ministry of Time, a newly established government department, is gathering ‘expats' from across history in an experiment to test the viability of time-travel. Commander Graham Gore (an officer on Sir John Franklin's doomed 1845 Arctic expedition) is one such figure rescued from certain death – alongside an army captain from the fields of the Somme, a plague victim from the 1600s, a widow from revolutionary France, and a soldier from the seventeenth century.

The expats are placed with 21st century liaisons, known as 'bridges', in unlikely flatshares. Gore has to learn about contemporary life from scratch: from air travel to industrial warfare, from feminism to Spotify, from cinema to indoor plumbing; and he must negotiate cohabiting with the ambitious modern woman who works as his bridge. After an awkward beginning, the pair start to find pleasure and comfort in each other's company, developing a relationship that is simultaneously tender, intense and profoundly unprofessional; and the expats, adrift in a new era, form friendships that ground and support them in the lonely 21st century, where they have outlived everyone they ever knew and loved.

When a deeper conspiracy at the Ministry begins to reveal itself, the bridge must reckon with what she does next. Will she save or sacrifice the exiled misfits she has come to care for so deeply?