Eva and Kat enjoy a carefree existence on their houseboat on a London canal. Until Eva's dream of becoming a mother is reignited by the death of their pet. Kat just wants to get a new cat. But when Kat's best friend, Roger, visits from Barcelona, they decide in a moment of drunkenness that he can be Eva's sperm donor. But what are the consequences for the lesbian couple, the biological father, the child and their relationships with one another?