Long ago in the cold lands of the far North, Balder, the God of Light once had a dream that he was going to die. He shared this dream with his mother, Freya, the Goddess of Love and Beauty. Frantic, she extracted oaths from every object in Nature of earth, water, fire and air, that it would never harm her son. Each gave its promise. And so, though a spear might be thrown at him, it would turn away because the wood had given its oath, and though a knife may be thrown at him, it too would turn away because the metal had given its word not to harm him. The Gods, of course, had great sport in throwing things at Balder.
Loki, the mischief-maker, soon found a loophole, however. For mistletoe, which has no roots of its own, did not fit into any of the realms from which Freya had extracted promises. So, Loki made a dart from a bit of mistletoe and gave it to Hoder, the God of Darkness, Balder’s blind brother and guided his hand so that the dart struck true and Balder was slain.
The Goddess Hel took Balder’s soul to the underworld, and despite Freya’s pleading, would not agree to release him. Finally, she said that if all of earth would cry for him, she’d let him go. So all the world cried for Balder for three days, but Loki transformed himself into a Giantess and when she (he) was asked to cry for Balder, he (she) flatly refused.
Here many folklorists would end the story, but there is an alternate, happier ending…
But the tears of Freya so touched the mistletoe, that its red berries turned white, bringing Balder back to life. Freya was so overjoyed that thereafter she kissed everyone who walked under the mistletoe out of gratitude for getting her son back.
As for Loki; he’s been chained underground ever since and there he will remain until the time of Ragnorak.