The Alternative Factor

Did You Know?

• John Drew Barrymore was cast as Lazarus, but failed to show up for filming, without explanation; the part was quickly recast with Robert Brown.
• The producers filed a grievance with the Screen Actors Guild, which suspended Barrymore's membership for six months, preventing him from working as an actor during that time.
• The special effects for the extra-dimensional winking episodes were achieved by superimposing a moving photograph of the Trifid Nebula over the action.

Plot

The Enterprise suffers a sudden energy pulse. Spock reports the planet's gravity dropped to zero and space briefly vanished. Sensors detect a human who was not there before. Kirk and Spock beam down and discover a single-person spacecraft. A disheveled man named Lazarus appears, falls off a cliff, gets hurt, and is taken to the Enterprise for medical care. Back aboard, Lieutenant Masters tells Kirk the warp drive's dilithium crystals have been drained. Starfleet contacts the ship, reporting that every quadrant experienced the same space-winking effect and electronic disruption. Fearing an invasion, Starfleet orders all vessels except the Enterprise to leave the area, and Kirk must find the disturbance's source.

Lazarus repeatedly fades in and out of existence, meeting a lookalike enemy inside a dimensional corridor, which causes the energy wink. Spock identifies a rip in space-time on the planet. Lazarus claims his enemy is trying to destroy the universe and needs dilithium crystals to repair his ship and continue the fight. Kirk refuses. Lazarus steals dilithium from the Enterprise but is caught. He denies the theft, blaming his nemesis. Kirk beams down to the planet with Lazarus and a security team to find the enemy. Lazarus experiences another dimensional corridor episode and is returned to sickbay. He then tells Kirk he is a time traveler, his ship is actually a dimensional corridor gateway, and the planet was once his home world. He says his enemy destroyed his civilization long ago, and he has chased that enemy for centuries.

Kirk notices Lazarus seems to leap between states: one moment wounded and insane, the next strong and rational. Kirk and Spock realize the truth: Lazarus is two different beings. One, from this universe, is insane; the other, from an anti-matter universe, is rational. They hypothesize that Lazarus's enemy is actually his own counterpart from the anti-matter universe. If the two Lazaruses ever make contact outside the dimensional corridor, within either physical universe, both the matter and anti-matter universes would annihilate each other.

Reception

Zack Handlen of The A.V. Club, reviewing the episode more than four decades after it first aired, assigned it a C−, calling the story baffling, unrewarding, and poorly paced. Hollywood.com’s ranking of all original series episodes put it at 77th out of 79. In 2017, Den of Geek listed it as the sixth worst episode of the original series. CNET, in 2016, placed it ninth worst among all Star Trek episodes, based on audience and host rankings at a 50th anniversary convention in Las Vegas.