"Lonely Among Us" is the seventh episode of the American science fiction television series Star Trek: The Next Generation, which originally aired on November 2, 1987, in broadcast syndication in the United States. It was written by D. C. Fontana, based on a story by Michael Halperin. It was the first episode of The Next Generation to be directed by Cliff Bole.

Set in the 24th century, the series follows the adventures of the crew of the Federation starship Enterprise-D. In this episode, as the ship is en route to an interplanetary conference with delegates from the Selay and Antican races on board, a non-corporeal alien entity takes possession of various Enterprise crew members, including Captain Jean-Luc Picard (Patrick Stewart).

This episode marked the first appearance of Star Trek: Deep Space Nine recurring cast member Marc Alaimo in a Star Trek series, as well as the second appearance of Colm Meaney who would later play The Next Generation and Deep Space Nine character Miles O'Brien. The Antican and Selay make-up was created by Michael Westmore from designs by Andrew Probert. Following the airing of the episode, fans wrote in to complain about a scene referencing cannibalism. Reviews were mostly negative, with criticism directed at the writing in particular.

The Enterprise is en route to the planet "Parliament" with delegates from two warring planets in the Beta Renner system, the reptilian Selay and the canine Antican, when the ship encounters a strange energy cloud. Unseen by the crew, Lt. Worf (Michael Dorn) is hit with a strange energy discharge as the ship passes the cloud, causing him to become violent. Doctor Beverly Crusher (Gates McFadden) sedates Worf and brings him to the sick bay, but is also infused with the energy as she examines his body. Crusher begins to act oddly to those around her and goes to the bridge, asking questions about the ship's navigational functions. When she questions Lt. Cdr. Data (Brent Spiner) at one of the science stations, the energy sparks between her and the console, leaving her confused as to why she is on the bridge.

The ship suddenly begins to malfunction and Captain Picard sends Assistant Engineer Singh (Kavi Raz) to investigate the cause. Singh is later found dead near a computer link, and Picard orders a murder investigation, considering the alien delegates to be prime suspects. Data investigates the murder in the manner of fictional detective Sherlock Holmes, and determines that the delegates were not responsible. Meanwhile, Counselor Deanna Troi (Marina Sirtis) uses hypnosis on both Worf and Crusher, finding that both recall being invaded by some entity during their blackouts. The ship suddenly drops again out of warp, and as Picard investigates the readouts at a bridge console, the strange energy transfers into him. The bridge crew becomes suspicious of Picard's actions after noting that all Enterprise systems are back to normal and that Picard has ordered them to return to the cloud.

The senior officers attempt to plead with Picard to undergo a medical examination and to step down from command, but he refuses. When they return to the cloud, Picard announces that they had picked up an entity previously when they passed the cloud, and now Picard and the entity are one. Under its influence, Picard plans to transport his energy back into the cloud, and he shoots energy at the bridge crew when they try to stop him. The crew are unable to prevent Picard from beaming off the ship. The crew spend hours trying to locate Picard to no avail, so they are forced to accept he is beyond recovery and prepare to leave. However, Troi senses the Captain's essence nearby, and Picard manages to signal the crew through the ship's computers. Data is able to reverse the transport, reconstituting Picard without the entity. After determining that Picard is himself again, lacking the memories since he was taken over by the entity, the Enterprise continues on to Parliament.

The original story by Michael Halperin contained a different subplot involving a problem with the dilithium in the warp drive of the Enterprise. The diplomatic conference was added by D.C. Fontana when it was developed into a teleplay. Fontana had previously worked on Star Trek: The Original Series, including the episode "Journey to Babel". "Lonely Among Us" was subsequently compared to "Journey to Babel", which Fontana denied, saying, "I wrote 'Journey to Babel' and I wrote this too, and I feel there is a difference. There's a definite delineation and separation here, both in intent and content." Director Cliff Bole did not recall much of the episode later, but did not think much of the script, saying "The subject matter affects the end product. There's some better written shows, obviously." It was the first episode of The Next Generation to be directed by Bole, who had previously worked on shows such as V and The Six Million Dollar Man.

Colm Meaney made his second appearance in The Next Generation after he originally appeared in the pilot, "Encounter at Farpoint", as a conn ensign on the bridge. In this episode he played a security ensign, as it was not until season two that he began to play the recurring character of Miles O'Brien, who would later become a series regular on Star Trek: Deep Space Nine. Another Deep Space Nine actor who made his first Trek appearance in this episode was Marc Alaimo, who played an Antican who was unnamed on screen, but referred to in the script as Badar N'D'D. Alaimo went on to play several other roles in The Next Generation including as the Cardassian Gul Macet in "The Wounded", before being cast as Gul Dukat in DS9. John Durbin appeared as the Selay leader, and would also go on to appear as a Cardassian later in the series, as Gul Lemec in "Chain of Command". Kavi Raz played Assistant Engineer Singh, although as he was unavailable for a re-shoot, in one scene he was replaced by a wig on a chair.