Little Mys older sister, Mymble, comes to Moominvalley. At the same time two tiny creatures come there too, Thingumy and Bob, with a giant suitcase that they protect. Though they are not the only visitors, The Groke is not far behind.
Too-Ticky brings Ninny to Moominhouse. Ninny has been frightened so often by her aunt that she has become invisible. Moominmamma concocts an infallible remedy, but will that and kindness be enough? Stinky does his best to see to it that it doesn't.
Moominvalley is hit by a terrible storm, and an old sailing ship is wrecked offshore, finally sinking. Pirates have made it to the shore unhurt and trouble starts when the captain, a terrible villain, grabs Snorkmaiden and holds her hostage, demanding a new getaway ship from the people in Moominvalley. The Inspector is frantic and helpless, and it is left to Moomin to rescue her.
After a tremendous downpour, Moomin finds a very small dragon in a puddle. Smothering this most exotic of pets with love, he expects great devotion in return, but finds that love is a fickle thing indeed, and particularly difficult to contain in a glass jar.
Moomin and friends have a great time in the jungle. Suspiciously helpful, Stinky offers to get them some animals, too, so it will be more like a real jungle. He is as good as his word, but the animals that he provides are not exactly of the kind they had in mind.
The Moomins have befriended all the wild animals that Stinky let out of the zoo, and when the zoo-keepers come to take the animals back, the Moomins, aided by the Inspector, fend them off. But, also, the hot spell doesn't last.
The Moominfamily and their friends decide to take a boat trip to a Lighthouse. But when they get there the Keeper is gone and the light has not been lit for a very long time. What happened to the Keeper and why did he leave the Lighthouse?
The beautiful young girl whom Sniff rescued woke up and said she had come to see the Hemulen who, however, denies any knowledge of any young girls whatsoever - his only worry being that he gets no answer from the Federation of Botanists about a totally new plant he has discovered.
Moominvalley is peaceful, as usual. For once too peaceful, for there simply aren't any crooks there for the inspector to arrest...The Chief Constable informs him that the whole police station will be discontinued as totally unnecessary, and it seems to be up to Moomin and his friends to see it that there is something for the Inspector to do, after all.