Three's A Crowd is the 17th broadcast episode and 5th produced episode of British television series Joe 90.
Joe 90 receives the brain patterns of a lovely girl who has attracted his father's attention but is suspected of being a spy.
Professor McClaine finds his heart ruling his head when an extremely lovely girl named Angela Davis comes along to see him, saying she is an American reporter. He ignores the possibility that she may be an agent working for a foreign country - which she is, in fact - and is both flattered and interested to find that she is knowledgeable about electronics and that she finds him attractive. Joe 90 views the friendship with growing mistrust. So does Sam Loover, who is worried when given a report on their many meetings by the security people who have Mac under surveillance. But when Sam speaks to Mac about it, he draws a blank. Mac insists that his personal life is no concern of Sam's. Sam, however, finds a willing ally in Joe 90, who is given Miss Davis's brain patterns. When Sam begins to question him, it is almost as if Joe can read Angela's mind and his story of what he thinks she intends to do reveals that she is definitely a spy. He can clearly see her taking photographs of the laboratory and stealing vital plans, then driving to an aircraft waiting to take her to an unknown destination.