Topher is in London, where there is a terrorist threat, when Ka, his clever time-travelling cat, disappears. She leaves a message on his computer saying she has gone to Haegellisdom. In pursuit, Topher finds himself in an Anglo-Saxon village. A ministrel warns that a fearsome Viking, lngwar the Boneless, is on his way, but the villagers think it is 'only a story'. Can Topher persuade them to heed the warning? Can he and Ka change history?