Amal El-Mohtar and Max Gladstone collaborated on "This Is How You Lose the Time War" (£5), a sweeping, romantic, sci-fi epic. A single letter sparks a connection between rival time-travelling agents on opposite sides of a complicated war. The more they write to one another, the more they fall in love, but their bond could cost them both their lives, and the war still rages around them with no clear exit in sight.