Barclay's fear of transporters leads to an alarming discovery.
Lieutenant Barclay is afraid of using the transporter, because he thinks that he saw something strange in the beam during one of his transports. His colleagues tease him about it, but when he investigates, he discovers a hidden danger. He has to decide whether to trust his instincts and take a risk.
The story is a sympathetic look at a character who has been a figure of fun, and it makes his anxiety into a real strength. The episode combines a mystery with a human story, and shows that Barclay is a valuable member of the crew. It also gives the audience a view of the transporter that was rarely seen, and it adds depth to the shared world of the series.