All the Lovers in the Night follows Fuyuko Irie, a woman in her mid-30s who doesn't have nearly as many lovers as the novel's cryptic title may suggest; instead, she has almost no one in her life. Having recently quit her job at a publishing house, Fuyuko has become a full-time freelance proofreader, working from home. She has no connection to her family, who live in a remote village in the countryside; she has no partner, no friends, and now, no colleagues, except for her editor Hijiri, who she speaks to only on the phone.

When Hijiri invites Fuyuko out for drinks one night, Fuyuko's carefully ordered world begins to crumble around her. She sees in the confident, charismatic, extroverted Hijiri everything she is not, and she starts to examine her own life more closely. In an effort to do something different for herself, she attempts to enroll in a course at her local community ...