The title characters of both magazines, Wu Fang and Yen Sin, were Yellow Peril villains in the mold of Fu Manchu.

Each issue contained a lead novel, written by Donald E. Keyhoe (who later became famous as the author of The Flying Saucers Are Real), together with additional material.

The novels are set in a dark, fog-shrounded version of Washington, D.C. resembling the Limehouse of Sax Rohmer's Fu Manchu books.

Yen Sin, described as the "Yellow Doctor" and the "Invisible Emperor", combines the mysticism of the East with the latest devices of the West with diabolical results.

He is opposed by Michael Traile, a man who is incapable of natural sleep (owing to a bungled brain operation) and who has to resort to periodic yoga-like relaxation sessions in order to recharge his vitality.