Tarzan and the Lion Man (Tarzan, #17)

A great safari had come to Africa to make a movie. It had struggled across the veldt and through the jungle in great ten-ton trucks, equipped with all the advantages of civilization. But now it was halted, almost destroyed by the poisoned arrows of the savage Bansuto tribe. There was no way to return. And ahead lay the strange valley of diamonds, where hairy gorillas lived in their town of London on the Thames, ruled by King Henry the Eighth. Behind them came Tarzan of the Apes with the Golden Lion, seeking the man who might have been his twin brother in looks -- though hardly in courage!