While the migrant trail takes Hayden as far as Liberia and Rwanda, her book is not, chiefly, a compilation of field dispatches. Her most startling reporting on this most global of subjects is done from her London flat. And yet Hayden’s account is no less immediate or distressing for her physical remoteness. It is indeed that very remoteness that affords her such intimate access to her subjects, most of whom know her only as a Twitter profile picture.