"Imaginary Friend" is the 22nd episode of the fifth season of the American science fiction television series Star Trek: The Next Generation, the 122nd episode overall. Set in the 24th century, the series follows the adventures of the crew of the Federation starship Enterprise.

In this episode, a child's imaginary playmate threatens the well-being of the Enterprise.

This episode centers around a girl named Clara, who just moved to the Enterprise with her father. She is lonely, and creates an imaginary friend named Isabella to keep her company. One day, to her surprise, her imaginary friend appears, and seems real (though she makes herself invisible before adults see her). Increasingly, Isabella gets Clara into trouble by leading her into off-limits places, prompting Clara to leave her to go play with others. When Clara returns, Isabella is angry and says, "When the others get here, you can die like everyone else."

Clara works up the courage to talk to her father, who then talks to Captain Picard. The crew learns that Isabella is actually an energy-based life form whose home is the nebula outside the ship the ship has been exploring. Picard finds Isabella in the arboretum and talks to her about human parenting. Isabella argues that the adults were cruel to Clara, and Picard explains that rules are for her protection. Isabella is convinced, and allows the ship to pass safely through the nebula.

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