The White Wolf's Son — Michael Moorcock

One summer day in Yorkshire, young Oonagh von Bek finds herself on an extraordinary and perilous adventure. The earth outside her family home breaks open and she is chased into the subterranean realms of the Middle March by a pair of dangerous men.

Her grandmother and grandfather-Oona, the Dreamthief's Daughter, and Elric, the last sorcerer of Melnibone-follow, encountering other important avatars of the Eternal Champion and seeking Elric's son. Fanning out across the infinite realms of existence and time, they hope to stop Oonagh's would-be kidnappers, Gaynor the Damned and his allies. All paths will converge in the dark empire of Granbretan, a land of cruel tyranny and wicked magic, where defilers and murderers plan the ultimate arrogance: to re-create the entire Multiverse-and replace the Cosmic Balance with themselves as eternal overlords...