The cruel Merdrun, the greatest warriors in the void, have invaded Santhenar but their portal backfired and they're stuck on the tropical Isle of Gwine. They're desperately trying to regain contact with the Summon Stone so they can reopen the portal and begin the slaughter of humanity. The hideous Whelm hold Karan and Llian's daughter, Sulien, in the frozen south and plan to sacrifice her to the Merdrun to gain their favor. Karan races south in a stolen sky ship but fears she will be too late. Llian, hurled through another portal, sees the summon stone wake and knows the allies have but one chance to destroy the Merdrun — though it will involve an alchemical quest that has always ended in ruin, a mad invasion in untested sky ships with untrained pilots, then the most unequal battle in all the Histories.