Two people beam down to a mining colony. They introduce themselves as Captain Janeway and Tuvok. They obviously are not who they say they are, but the miners are unaware of any deception and agree to make a trade. "Janeway" promises to beam down a supply of dilithium in exchange for a load of bolomite. She and "Tuvok" are well-practiced in their roles and knowledgeable about their characters; the miners trust them and are impressed with their generosity- "Janeway" says she plans to use the bolomite to help a colony of orphans. Back aboard their ship, "Janeway" and crew receive their shipment and speed away before delivering the dilithium they promised the miners. The scam was a success.
Meanwhile, on Voyager the genuine crew is having problems. A faulty component in Neelix's galley has disrupted systems all over the ship. It seems he picked up the component as a trade, in exchange for a load of supplies that he sent to a shelter for orphans, and failed to test it before installing it. In the middle of the mess the ship gets a call from Orek, the head of mining operations at a nearby planet. He is angry that Janeway has run off without dropping off the dilithium she had promised him. Naturally, she has no idea what he's talking about.
Orek shows her a recording of "Janeway" making the agreement with the miners. At the mention of orphans, an annoyed Janeway starts putting the pieces together. She sits Neelix down and listens as he explains where he got his kitchen component. He and Paris encountered a nun called Dala a few weeks back, and got to know her and her companion Mobar (a pair who look suspiciously like "Janeway" and "Tuvok"). They brought the two on board the Delta Flyer to negotiate a trade, giving them an opportunity to surreptitiously download information about Voyager. They then used what they had learned to pose as Janeway and Tuvok.
Orek agrees to let Janeway hunt down the impostors, who happen to be right in the middle of cheating someone else. Once the victim realizes he is being tricked he seizes Dala's ship. Believing Voyager is in on it he fires at it as well. The real Janeway beams her doppelganger into the brig and gets away.
Neelix picks up the prisoner, trying to find a spark of honesty in her. Just as he appears to be making friends with her, she grabs his phaser and runs. Already familiar with the layout of the ship and the workings of the Delta Flyer, she escapes before anyone can catch her and returns with the Flyer to her co-conspirators. Having predicted her actions, Paris and The Doctor emerge from their hiding place on the Flyer and wait.
The thieves run. They return to the caves where they have stashed all the booty they've stolen from their numerous victims. Dala then surprises her cohorts by turning on them. She subdues them with a weapon and then contacts Voyager, which is waiting for her call. When her fellow thieves demand an explanation she activates her mobile emitter- she's The Doctor in disguise. The real Dala awakens on the Delta Flyer, where Paris holds her at bay.
Voyager returns all the stolen goods to their rightful owners.