Pangea, and almost back

In this time-traveling adventure, Freddie O'Toole is searching for his father, who has disappeared in a plane crash several years earlier. His guardian sends Freddie on a secret expedition to Timor where Freddie and his crusty manservant, Gruntenguile, are chased by Snapahuti headhunters. After a narrow escape, they discover portals that take them back to Pangea and then to ancient Africa where Freddie becomes a contestant in the Tournament of Blood.