Seconds later, Riker and Worf enter the Turbolift to find Data and the bleeding, unconscious Troi. Data immediately attacks Riker, but suddenly realizes what he is doing and stops. Later, he tells Picard and the crew that he had an uncontrollable urge to eliminate the image of a mouth that he saw on Troi's shoulder — an image first seen in his dream program. Since the dream program has been turned off, no one understands why these images are still appearing, so Geordi suggests taking time to conduct a sub-polymer scan of Data. In the meantime, Picard orders him confined to quarters. Meanwhile, in Sickbay, Beverly discovers a strange interphasic rash on Troi's shoulder near her stab wound. She brings Picard in to see the rash, which is quickly getting worse, and upon examining Troi with an interphasic scanner, realizes that she — and most of the rest of the crew — are covered with leech-like creatures.

Soon afterward, Beverly grimly reports that the creatures are extracting their cellular peptides and will eventually destroy them if they are not stopped. Unfortunately, stopping them is impossible since the organisms exist only in an interphasic state beyond normal vision or sensor acuity. Everyone is at a loss, until Picard realizes that the images Data has been seeing in his nightmares, like the "mouth" on Troi's shoulder, correspond with the actual locations of the creatures. He decides to link Data's neural net to the Holodeck so they can observe his dream images. Geordi hooks Data up and Data activates his dream program, and Picard and Geordi then enter his dream. They see the "Troi cake," meet Sigmund Freud and encounter the workmen, who reveal the warp plasma conduit. The workmen attack Picard and Geordi, and Data makes a shrieking noise that causes them pain. The dream somehow makes sense to Data, and he wakes up and he Instructs Geordi to adjust his positronic subprocessor to emit an interphasic pulse, theorizing that the high frequency pulse will eliminate the creatures. The plan successfully drives away the creatures, who were also disrupting the warp drive, leaving Data with an increased appreciation for his "human" gifts.

Commander William T. Riker: Something wrong, sir?
Capt. Picard: I just got a message from Starfleet Command.
Commander William T. Riker: Bad news?
Capt. Picard: You could say that, I've been invited to the annual Starfleet Admiral's banquet.
Commander William T. Riker: My condolences.
Capt. Picard: I've managed to avoid it for the last six years. I guess my luck just ran out. I can't imagine anything more tedious. Fifty admirals shaking hands, making dull conversation, uninteresting food, boring speeches.
Commander William T. Riker: Can't you find an excuse not to go?
Capt. Picard: After six years, I don't have any excuses left. Besides, I've been invited by Admiral Nakamura, the Sector Commander. He'd consider it an insult if I turned him down.
Commander William T. Riker: We could cause a diplomatic crisis. Take the ship into the Neutral Zone and attack the Romulans. That should get you out of the banquet.
Capt. Picard: I wouldn't count on it.

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Lieutenant Worf: Mmm. It is delicious.
Lt. Cmdr. Data: What kind of cake are you eating?
Lieutenant Worf: It is a cellular peptide cake... with mint frosting.