Thiassi was an icegiant who was a master at changing shape.  He frequently
journeyed across the mountain walls, riding the cold winds in the shape of an
eagle.  Sharp-eyed and fearsomely taloned, he was a formidable predator.

The god that Thiassi chose to challenge was Loki, the trickster, who happened
to be idling about in the world of man.  Thiassi looked down at him from the clouds and saw that he was roasting an ox and dived down and snatched it for himself.  Loki saw him coming and, like lightning, the god struck back. He buried his battlestaff in Thiassi's feathered bosom.

High above the trees he flew, rolling and tumbling on the wind, wrenching Loki's arms in their sockets.  He dropped lower and dragged Loki trough the tree branches, into mountain lakes, and across hillsides bristling with gorse.

When Loki screamed that he surrender and would give anything for his freedom, Thiassi desist.

" Bring me the apples of Idun," he said, and released Loki.  This was no easy
task for the apples gave eternal youth - once fed on them, a giant might achieve immortality.

Loki who had no sense of loyalty and whose only concern was for himself, did as he was told.  He told Idun that he came across apples to match her own, in the grove in Midgard.

Idun followed Loki into the world of humankind, where the eagle Thiassi waited. He caught her up in his talons and flew into the clouds, heading for his mountain aerie.  Loki returned to Asgard, saying nothing about what he had done.

The theft was noticed at once, for the heavens began to fade and wither. Loki did not know that a servant overheard everything he had said to Idun. The servant told the gods what he heard and they ordered Loki to find Idun and bring her home.  No-one knew how he found her but Thiassi was caught and
Idun was set free by Loki.