In 1968, English businessman Donald Crowhurst is inspired by Sir Francis Chichester to compete in the Sunday Times Golden Globe Race, a single-handed, round-the-world yacht race. Though only an amateur sailor, Crowhurst believes that technology and gumption will enable him to succeed in a custom trimaran, thus ensuring financial security for his wife and young children. As delays and costs mount, his main sponsor, Stanley Best, becomes so nervous that Crowhurst is forced to sign promissory notes pledging his company and home to Best. Sailing away in the Teignmouth Electron, Crowhurst must complete the race or lose everything he holds dear.
Crowhurst arranges sponsorship and a press agent to promote his voyage and he is also supported by his family. During his trip he attempts to give an optimistic version of events to both his family and press agent but inwardly he is feeling under pressure due to his financial situation, the dangers he is encountering and his loneliness. The film cuts between his voyage and scenes at home where his wife Clare is attempting to deal with the situation.