"Clues" is the 14th episode of the 4th season and was written by Bruce D. Arthrus and Joe Menosky.
The Enterprise is investigating a star system when it encounters a wormhole. Everyone is knocked unconscious except Commander Data. He tells the crew upon awakening that everyone was out for 30 seconds and says he'll readjust the ships instruments that were put off line during that time. A probe is launched to get information from the star system after Data suggest it may be too dangerous to take the ship in further.
Dr. Crusher notices an experiment with a rare moss is showing at least 24 hours growth and brings it to the captain's attention. Counselor Troi experiences dizziness and hallucinations, claiming she saw someone else in her reflection in the mirror. Worf complains of pain in his wrist and tells the doctor that he reported to sick bay to report anything out of the ordinary. It is revealed that his wrist was broken but has no memory of it.
In the meantime, Data is the only one who seems to be hiding something. He gives evasive answers to inquiries and can't explain the false readings from the launched probe---showing information from another system not related to the area of space.
While he is under investigation, the ship heads back to the system to uncover the mystery. An energy source penetrates the shields and possess the counselor. She confronts Data about their failed plan. Then Geordi tells Data that he's wanted on the bridge.
Data tells the captain that they must leave the system immediately. Picard demands to know why and asks if anyone gave him an order to suppress information about the star system. Data stuns the captain when he said "You did, Sir."
The alien enters the bridge and confronts the crew saying that the Enterprise must now be destroyed about it failed to live up to their end of the agreement, which was to leave the system and leave them in peace. As Data explains, they are called the Paxans and they are xenophobic in nature and want to be left alone without outsider knowledge of their existence. We see the story played out as Data relays what happened in their first encounter and learn that the alien boarded the bridge and was confronted by Worf. The alien overpowered him and his wrist was broken. The Paxans required at least 24 hours to complete a memory sweep of everyone on board the ship so they'd forget about their encounter.
Picard convinces the alien to try it again and the crew would ensure they would not leave any clues behind this time. "You are a most unusual species," the alien tells Picard, but "worthy of a second chance."
The crew is once again knocked unconscious and awakened but this time Picard is convinced by Data's reasoning to leave the system because it may pose a threat to the ship. The scene ends with a satisfied smile on Data's face.
This was a fun episode, partly because we get to see Data acting suspiciously and not knowing if it's alien influence, a positronic brain malfunction, or that he's deliberately lying. And if he is, why? The story is full of suspense from start to finish, leaving the viewer waiting for the next clue in the mystery.