Stellamaris is a young paralysed girl who is confined to a bed in the Channel House overlooking the English Channel. She is cared for by her elderly uncle and aunt, Sir Oliver and Lady Blount and is often visited by two young men, John Risca, a journalist, and Walter Herold, an actor, who regularly visit the house from London and who entertain her by weaving fantasies around an imaginary castle and land. After some time, Stellamaris starts to recover the use of her limbs and the book tells the story of the changing relationships between her, John and Herold as well as Unity, a young girl who John rescues from the grimmest of circumstances, as their fortunes twist and turn.