Yasmini Series by Talbot Mundy

Captain Athelstan King of the Indian Secret Service, with India in his blood for seven generations, is attacked with a knife to prevent investigating rumors of a gathering force above the Khyber Pass waiting to engulf the British. Yasmini, beautiful, clever, exquisite dancer, mistress of many languages, has access to the caves where other spies have vanished. "The entrance to the Khinjan Caves is free to any man who can tell a lie without flinching. It is the way out again which is not free."

Yasmini, the Indian princess who has had a part in others of the author's tales is the heroine of this story, and a young American couple have a part in the action. Intricate plot and picturesque settings.

Athelstan King (hero of Mundy's early classic King -- of the Khyber Rifles) and burly and down-to-earth American Jeff Ramsden follow the gray mahatma through a series of caves beneath an ancient temple, revealing different levels of wisdom and the limitations and tortures of those stranded at any one level. And at the end of their quest through this Dantean Inferno waits death . . .