S01E75: The Fabulous Emerald

Moomin is beset by strange, recurrent dreams in which he is urged to go to a far-away waterfall and look for something. At last he sets out with Snufkin, and they make a most unusual find that Moomin can't really make anything of. But dreams sometimes have a meaning, and when a terrible hailstorm shatters the Hemulen's greenhouse and destroys all his plants, Moomin's find comes to play a most important role.