The two-part Season 5 finale and Season 6 premiere of Star Trek: The Next Generation is one of the series' most ambitious time-travel stories — a Victorian-era romp that brings together Guinan, Mark Twain, Data's severed head, a cavern full of alien parasites, and a snake-headed cane that opens portals through time. It won two Emmy Awards and remains one of TNG's most rewatchable outings.
The Enterprise is recalled to Earth after an engineering team discovers something impossible in a cavern near Starfleet Headquarters in San Francisco: Data's severed head, buried among 19th-century artifacts and estimated to be approximately 500 years old. Data examines his own future remains with characteristic calm — noting 12% decomposition of bitanium in the neural pathway links — and concludes that at some future date, he will be transported back in time to Earth, where he will die. When Riker says they'll do everything they can to prevent it, Data replies with quiet acceptance: "It has occurred. It will occur." [1][2].
The investigation reveals cellular fossils native to the planet Devidia II, indicating a race of shapeshifters visited Earth's past. The Enterprise travels to Devidia II, where a temporal disturbance is detected. Troi senses human lifeforms, but no one is visible. The crew determines the aliens are slightly out of phase with time. Data, whose android body has a phase discriminator, is the only one who can see them [1][2].
Inside a cavern on Devidia II, Data adjusts his phase and describes what he sees: vaguely humanoid creatures, two to three meters tall, silver-grey, with an orifice in their foreheads, absorbing light strands from a device in the center of the room. The light strands are human life forces — harvested at the moment of death. When two aliens enter a time portal, Data is pulled in [1][2].
The cavern becomes the story's central set piece — both on Devidia II and its 19th-century counterpart near San Francisco, where the aliens have been posing as cholera victims to mask their predation on humans. Dr. Crusher connects the dots: the Devidians use the cholera epidemic as cover, draining neural energy from the dying [1][2].
The Devidians carry a cane-like device with a snake's head — a portable time portal generator. This is the story's MacGuffin and its most important prop. The staff opens a temporal vortex between 1893 San Francisco and Devidia II in the 24th century, allowing the aliens to travel back and forth across five centuries. During the climactic struggle in the cavern, the staff is fought over, and in the chaos, Data's head is severed from his body. The away team follows one alien through the portal into the future, bringing Data's headless body and the staff with them [1][2].
In the 24th century, the staff is the key to resolving the crisis — but it can only transport one person back to the 19th century. The device becomes the mechanism by which the crew swaps places: Picard remains in the past while the rest of the team returns to the future [1][2].
The discovery of Data's head in the opening scene is one of TNG's most striking images — the android's familiar face, caked in five centuries of dirt, resting among Victorian relics. The image sets the stakes for the entire story: the crew knows Data will die in the past, and nothing they do can change that fact [1][2].
But Data's head becomes more than a plot device. When Picard is stranded in 1893 with no way to communicate with the future, he hides a message in Data's head — placing iron filings with a binary-encoded warning into the android's static memory. Five hundred years later, Geordi reattaches the ancient head to Data's body, and Data discovers the message, allowing the crew to find a solution. Picard's ingenuity — leaving instructions in a head he knew would be found centuries later — is one of the episode's most satisfying twists [1][2].
Data arrives in 1893 San Francisco and, needing money, wins a sizable amount in a poker game. He befriends a bellhop named Jack London (the future author, here a teenager working in a hotel) and enlists him to acquire supplies. Data is building a detector to locate the aliens [1][2].
Data sees a newspaper photo of Guinan — his 24th-century colleague from Ten Forward — and tracks her to a literary reception at her home. He assumes she has also traveled from the future. When she fails to recognize him, Data realizes: this Guinan is a young woman living in her own time, centuries before she will ever board the Enterprise. She is an El-Aurian, centuries old, and has not yet met Picard or any of the crew [1][2].
The reception's honored guest is Samuel Clemens — better known as Mark Twain, played by Jerry Hardin in a performance so beloved it launched a one-man Twain stage show Hardin performed for 15 years. Clemens is holding forth on Alfred Russel Wallace's theories about extraterrestrial life when Guinan suggests that Earth might be one of millions of inhabitable planets. Clemens is intrigued [1][3].
When Data pulls Guinan aside to explain his situation, Clemens eavesdrops from the doorway. He becomes obsessed with uncovering the truth about the two strangers. His suspicion drives much of the episode's comedy — Clemens follows Data and Guinan, accuses them of conspiracies, and eventually insists on accompanying the away team through the time portal to the 24th century, where he is astonished to find a future with no poverty, war, or prejudice [1][2].
Guinan's role is more profound. She convinces Picard that he must join the away mission back to the 19th century — warning him, cryptically, that if he doesn't, they will never meet. "Don't be so sure" she says when Picard says he remembers the first time they met. Her knowledge of the future — and her understanding that Picard's presence in 1893 is what will bring them together centuries later — closes a time loop that defines their relationship for the rest of the series [1][2].
"Time's Arrow, Part II" won two Primetime Creative Arts Emmy Awards at the 45th ceremony in 1993:
The hairstyling award recognized the period-accurate Victorian hair designs across the large cast of guest stars and background players. While not a makeup award per se, the hairstyling and costume work were inseparable in creating the episode's convincing 1893 atmosphere [4].
Jerry Hardin's Mark Twain makeup — designed by Doug Drexler, who would go on to win an Oscar for Dick Tracy — was Drexler's final makeup job for the series. The Twain prosthetics became iconic enough that Hardin built an entire stage career around the character [5].
The climax intercuts between centuries. In the 24th century, Geordi and Data discover that the aliens are absorbing human life forces and storing them as energy fragments. Using photon torpedoes phased with the alien habitat, they can negate the time-shift amplification that threatens 19th-century Earth. In 1893, Picard remains behind to tend an injured Guinan while the rest of the away team returns to the future through the staff's portal [1][2].
Clemens returns to his own time, settling Picard's debts and watching over Guinan. Picard laments not having the opportunity to know Clemens better. The author replies that who he is is written into his books. Picard returns to the future, reunites with Guinan on the Enterprise, and the cycle is complete [1][2].
See also: Guinan, TNG People, TNG Milestones.
[1] Wikipedia - Time's Arrow (Star Trek: The Next Generation)
[2] Memory Alpha - Time's Arrow (episode)
[3] TrekToday - Hardin: TNG Mark Twain Led To Own Show
[4] Wikipedia - Primetime Emmy Award for Outstanding Hairstyling