During shore leave on Akritiri, Paris and Kim are falsely accused of a terrorist bombing and sent to prison. Paris is already in the nightmarish alien jail when Kim arrives via a long metal chute. As if confinement in the brutal hellhole weren't bad enough, Paris shows Kim the "clamp" that every prisoner wears; it seems to affect the wearer's nervous system and it can't be removed.
On Voyager, Janeway is informed by Liria, the Akritirian Ambassador, that Paris and Kim have been imprisoned for a bombing that killed 47 people. The "proof" is traces of trilithium found on their clothes. Although trilithium can be made from the dilithium Voyager uses to power its engines, Janeway emphatically denies that her people were involved. She leaves, determined to find the real bombers.
Back in the prison, Paris and Kim plot how to escape through the chute, which is protected by a deadly forcefield. But before they can, Paris is stabbed by a brutal inmate. With no medical assistance available, Kim makes a deal with another inmate, Zio; he'll take Zio with him when he disables the forcefield in exchange for some supplies to clean up Paris's wound.
Back at the prison, Kim and Zio climb to the top of the chute, where they find that the opening is actually a docking port leading into space; what they'd thought was an underground jail is actually a large isolated satellite. With Paris getting closer to death, Kim tries to talk some of the inmates into cooperating in a prison break, but the idea seems so outlandish, they jeer at him. Later, when a delirious Paris disables the tool that Kim had used to neutralize the forcefield, Kim comes close to killing his friend. He regains his senses just in time.
Janeway tracks down and captures the real bombers, a young brother and sister, but she is shocked when Liria refuses to trade them for her people; he never reverses a conviction. Now the Captain is willing to deal with the bombers. In exchange for their freedom, the pair lead Tuvok and Janeway to the prison, where they extricate their officers and escape.