The Purple Death From Outer Space (1966)

Earthmen are suddenly stricken with a mysterious disease, which causes instant death and leaves a purple spot on the forehead of each victim. Investigating, Dr. Zarkov discovers a spaceship from Ming's kingdom on Mongo spreading a dust across Earth's atmosphere, which Zarkov correctly deduces is causing the plague. Accompanied by Flash Gordon and Dale Arden, Zarkov drives off the ship and hurries to the friendly Mongo kingdom of Arboria, to enlist the aid of Prince Barin. At Barin's palace, they meet Queen Fria and Count Korro of the ice-kingdom Frigia. Helping them rescue a Frigian general from Ming's palace, they learn the nature of Ming's plague-dust and its antidote, found only in Frigia. With Fria's blessings they fly to Frigia to obtain the antidote, accompanied by Arboria captains Ronal, Roka and Turan. But Ming learns this, sends his own officers Torch and Thong to stop them with raygun fire and an army of humanoid robots... [Unedited compilation of the serials Ch's 1-5 and the cliff-hanger resolution in 6].