'Like to spend a night in the Goblin?' The Swallows are staying on the Suffolk coast while they wait for their father to return home from China. But although the harbour is bursting with bobbing yachts, barges and steamers, this year there's no chance of any sailing for the landlocked Swallows. That is until they rescue young Jim Brading and his boat the Goblin from a sticky situation and to their delight are recruited as crew members. Mother agrees they can go, on one condition - they absolutely must not sail out past Beach End Buoy and into the open sea...