From rivals propelling each other forwards to friends combining their talents, it's clear: often two heads are better than one. How did William and Ellen Craft work together to pull off a perilous cross-country escape from slavery? How did the queer artists Marcel Moore and Claude Cahun become icons of the surrealist movement, then heroines of the resistance in the Second World War? Why couldn't Steve Jobs have started Apple alone? Vibrant, feminist and unexpected, Cathy Newman rewrites the history books to expose this strange power of two - and to ask why certain collaborators are so often left out of the narrative.