Marvel Novel: Legends of Asgard - The Head of Mimir (Heimdall Trilogy #1)

 It is a Dark Time for Asgard.The All-Father is trapped in a bewitched Odinsleep, inspiring an all-out assault from the Frost Giants. They evade the gods' defenses with uncommon ease, as if guided by augury.

Heimdall, a quick-witted young warrior still finding his place amongst Asgard's defenders, believes it no coincidence that Odin lies enchanted and that the Giants are so well-informed. Sneaking into Odin's inner chambers, he discovers that the severed head of Mimir, a great source of wisdom, is missing. Accompanied by his sister, Lady Sif, Heimdall must quest across the Ten Realms to retrieve it, lest mighty Asgard fall.