The story begins when there's a holodeck malfunction during Data's rehearsal for Shakespeare's The Tempest. The Orient Express shows up and Data and Captain Picard jump out of it's way right in the nick of time.
As the crew investigates a system for habitable planets, the ship suddenly goes into warp drive on its own. But it's fortunate that it did because dataflux distortions were accelerating and would have destroyed the ship. Geordi enters a jeffries tube and finds a new circuit node that's connecting other systems of the ship together and is protected by a force field. Further scans show more nodes generating around the ship.
The crew decides at first to regain control of the ship and enters the holodeck where the problem began. They find several different programs running at once and characters appear and act protective of the ship and prevent Data from gaining access the holodeck circuitry as a train conductor demands tickets from them.
Data notices that pattern of the nodes is consistent with the matrix of his positronic brain and that the ship is forming an "emergent property," or a form of life consisting of all the ship's components including the crew's logs, technology, and holodeck programs.
At this point, Captain Picard decides to find out what the new emergent life form is trying to do. Counselor Troi, Worf, and Data reenter the holodeck to interact with the characters to get more information. Once more, the conductor wants their tickets. A mafia character leaves the train and carries a brick up through a subway and Dianna and Worf follow him as he puts the brick into a wall to "lay the foundation."
Meanwhile, Data attempts to disengage the nodes. A taxi also runs him over and the ship begins losing structural integrity. Data is forced to stop his attempt. Geordi finds an emergent lifeform in the cargo bay that's generating energy within it's core.
Worf, Troi, and Data try again to communicate with the holodeck characters as they focus on getting to "Vertiform City." The ship is heading toward a white dwarf star and the ship uses its tractor beam to get vertiron particles. When it fails to gather enough vertiron particles, the ship heads in a new direction as the train conductor takes the train in a new direction.
The crew decides to create vertiron particles in a nearby nebula to avoid the ship using all it's reserved power to get to "New Vertiform city." The crew watches as the new life form takes in the vertiron particles and phases out through the ship into space. Later, Captain Picard and Data discuss the risk they took in helping the new life form exist even though the end result was unknown. As Picard explains to Data, the new life was born from the sum of The Enterprise's parts and therefore the chance of the new life being malevolent was not very likely.
I liked this episode because it had a lot of images that were quite like dream symbols and reminded me of "Phantasms" and "Birthright." It also reminded me of another good episode "Home Soil" in which the Enterprise crew discovers an unknown life form and works to communicate with it and learns that their experiments on a dead planet were actually killing the species. Rather than eliminate the species for convenience and safety sake, they work with it to ensure it's survival. That theme is repeated here and sends a positive message about respecting other life forms.