Voyager encounters a contained ocean in space which resembles a planet, owned by the Monean Maritime Sovereignty, an advanced civilisation comprising 47 regional sovereignties. When Riga, assistant to the Monean consul, explains that the ocean is losing containment (7 per cent in the last year alone), the Delta Flyer takes him to investigate the ocean centre. As the Delta Flyer submerges, the Voyager crew run a computer simulation from which they estimate the ocean will suffer complete loss of containment in less than five years. Voyager plans to reinforce a breach in the containment field with a deflector beam but instead the Delta Flyer manages to stabilise containment temporarily with a power transfer.

When Paris claims that with a few simple thruster modifications and immersion shielding the Delta Flyer can be made seaworthy "in no time" Janeway responds that it would take a week to make the same modificiations to Voyager.

The Monean world was actually formed over a 100,000 years before Voyager's arrival, and therefore over 99,700 years before the Moneans' discovery of the 'planet', by the use of a kinetic transfer system to draw the water around a core reactor. The Delta Flyer crew determine that it is the Moneans' mining operation which is gradually destroying the ocean by extracting oxygen from the water, as this forces the core to transfer power from containment to keep from being crushed by the added density of the ocean. Janeway offers the Monean consul several permanent solutions that would make the refineries obsolete, but he only plans to include them as suggestions in a subcommittee report. Believing that the Moneans will take no action, Paris goes against orders to disrupt the Moneans' internal affairs and secretly takes Riga, a Monean, in the Delta Flyer to take the oxygen refineries offline. When Paris refuses Janeway's order to desist, she orders a photon torpedo readied. Once they reach the reactor, Paris launches a torpedo at the same time that Voyager does, and the two torpedoes meet and explode just short of their targets. Paris is brought back to the ship, demoted and confined to the brig for 30 days.

The brig is seen extensively in the episode. It is also seen in several other episodes, particularly [#32 Meld], [#70 The Gift], [#141 Live Fast And Prosper], [#150 Repression].

brig - holding cell

brig - doors onto corridor, ceiling and control console

Tuvok modifies a photon torpedo to act like a depth charge.

With a few simple thruster modifications and immersion shielding, Paris claims the Delta Flyer can be made seaworthy in no time. During the Delta Flyer's reconnaissance of the ocean centre, it travels to 600 kilometres beneath the ocean surface. A sea creature, which Kim likens to an electric eel, and which Paris says is a hell of a lot bigger, attacks the Delta Flyer, with one strike generating 500,000 volts. As a result the Delta Flyers shields are "fried", and thrusters are offline. The hull breaches and water leaks in; Paris seals the hull. They lose communications, shields and propulsion. After conducting a power transfer for stabilise the ancient reactor and thereby seal a containment breach in the ocean world, the Delta Flyer crew reduce the ship's density by venting plasma and transporting all non-essential equipment off the ship so that the ship will rise to the surface. The Delta Flyer's slow ascent is detected by Voyager.

Sometime during the 30 days Paris is confined to the brig, the ship is attacked without warning by five ships of unknown identity or origin.