While on holiday in Greece, middle-aged college professor Leda Caruso (Olivia Colman) meets Nina (Dakota Johnson), a young mother, when Nina’s three-year-old daughter Elena goes momentarily missing on the beach. Leda finds Elena and returns her to Nina, who expresses her growing exhaustion and unhappiness. Elena is upset after she loses her favorite doll, which Leda has taken on purpose. In flashbacks, it is revealed that young Leda (Jessie Buckley) also struggled with being a young mother to her two daughters, Bianca and Martha, often losing her patience and becoming withdrawn.
One evening, Leda has dinner with Lyle (Ed Harris), her hotel’s caretaker, who sees that she has the doll but doesn’t comment on it, nor does he tell Nina. Leda later discovers Nina is having an affair with Will (Paul Mescal), an assistant at the resort, and Nina explains her husband Toni is very controlling. The search for Elena’s doll continues, with Nina even putting up flyers offering a reward to whoever can return it to them.
At a market, Leda buys Nina a hatpin to help hold her sunhat in place. When Nina asks Leda about her daughters, Leda becomes emotional. She reveals that she had abandoned them for three years after she became too overwhelmed with being a grad student and a young mother, leaving them with her now ex-husband, during which time she had an affair with a fellow professor (Peter Sarsgaard). She admits that being away from her daughters felt “amazing”, and she only went back to them when she genuinely missed them. Nina learns that Leda knows about her and Will, and Will later asks Leda if they can borrow her apartment to have sex.