Tarzan and the Gauntlet of Vengeance

Clayton's sister (or rather her valet, Hobson) kidnaps Jane, Tantor, Terk, and the Professor, placing each in a separate, deadly peril. She then injects Tarzan with a fatal poison (via blowdart) and informs him that the antidote lies far away on a distant mountain she's dubbed ""Clayton's Peak"". He, therefore, has a choice, she says -- to suffer as she had (and lose those he loves) or as Clayton had (and lose his own life).