The Venus Trilogy - Complete Sci-Fi Series: Planet of Peril, Prince of Peril & Port of Peril

The Planet of Peril tells the story of Robert Grandon, a restless young man who gets kidnapped by a mysterious scientist Dr. Morgan and finds himself transported to the planet Venus in the distant past in the body of a Venusian prince who has been enslaved by a beautiful and tyrannous Empress. After he manages to escape, Grandon starts his rise to leadership of an army of rebels.
The Prince of Peril – Using his secret method Dr. Morgan projects a young Martian's astral body into a certain Harry Thorne on Earth, who then gets transported to an ancient Venus. He arrives there in the body of Prince Zinlo of Olba, and he is soon forced to escape assassination, since an ambitious noble is killing off the Royals in a bid to seize the throne. With the help of the fellow interplanetary traveler Vorn Vangal he gets to know the planet and the rules of it.
The Port of Peril – Robert Grandon and his Venusian wife Vernia, empress of Reabon were about to start their honeymoon when the terrible yellow pirates, lead by Huitsenni, kidnapped Vernia and took her to their hidden port. Grandon goes on a quest to save her, a quest that will put him on challenges, and against enemies beyond everything he had came across before.
Otis Adelbert Kline was an adventure and science-fiction novelist, best known for his interplanetary adventure novels set on Venus and Mars, which instantly became science-fiction classics.