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?

Although these thirty-somethings aren't following a conventional path, this bittersweet drama full of comic notes depicts modern characters without stereotyping them. It throws up questions faced by everyone in their thirties. What kind of parent would I be? What does it mean to start a family? The fairytale London canal is also a character in itself. As the seasons change, the flowing water changes too – just like relationships and life itself.