It's 1979, and 13-year-old Lydia has no idea how she'll cope when her dad announces that the family has to sell up and move onto a Thames sailing barge in Essex. With his girlfriend. And her three kids. Between trying to keep her clothes dry in a leaky cabin, disastrous hair-dye attempts, awkward encounters with local boys, and coping with her suddenly enormous and troublesome family, Lydia fears she'll sink rather than swim.