David Phillips (Patrick Macnee) is running down the darkened streets of London's Limehouse district, pursued by two men with guns. He finds a public phone and puts a call through to Dick Barton (Don Stannard), but before he can report, a shot rings out. Barton must piece together what Phillips found out that got him killed. Phillips had been assigned to protect Professor Mitchell (Percy Walsh) and his new development, a ray capable of exploding any unstable element aboard an aircraft in flight. Mitchell has been targeted for kidnapping by Serge Volkoff (Meinhart Maur), a foreign agent from Eastern Europe, as part of a larger, much more sinister plot to destroy England and cripple Western Europe. Complicating matters further is that Mitchell's daughter (Joyce Linden) has also been kidnapped, and Barton must contend with Volkoff's crafty female companion Anna (Tamara Desni).

Government agent Dick Barton battles a ring of Nazi spies who are planning to poison the entire London water supply.

Someone is stealing priceless paintings from the great museums of the world and replacing them with nearly flawless forgeries. Leonardo da Vinci's "Madonna and Child" is being shipped to London's Tate Gallery for a special exhibition, and Paul Mitchell is assigned to protect it. Upon the painting's arrival, Paul realizes it has been switched. Eager to collect the museum's $50,000 reward, he teams up with Mary Mason, a Tate employee, to recover the original.

When various trustees of the Van Traylen Orphanage begin dying in close order, it's at first written off as a coincidence. But, when a school bus accident very nearly takes out three more of them along with a group of orphans, Col. Bingham and his pathologist friend, Mark, begin looking into the deaths. They come to think the answer lies with one of the girls on the bus, who has vivid memories of things she could not possibly have seen.

Following an explosion in a laboratory accident, physicist Colin Trafford is sent to a parallel universe where he enters the body of his counterpart, a popular writer married to an attractive woman who hates him.