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the starship USS Enterprise arrives at the planet Sarpeidon to evacuate its inhabitants, who are threatened by the impending supernova of their sun. Sensors detect no signs of humanoid life on the surface. Kirk, Dr. McCoy and Spock beam down to investigate.

The landing party finds a sophisticated computer library maintained by a man named Atoz. Atoz explains that the library is an archive of historical data disks. Kirk warns Atoz of the planet's imminent destruction. Atoz says he is aware of this, and that he is already prepared and will join his family soon. He demonstrates a machine called the Atavachron, a time portal linked to the library viewers. Viewing a data disk tunes the Atavachron to the era recorded on the disk.

Kirk hears a woman's scream through the portal. He reflexively rushes to her assistance and disappears through the portal. McCoy and Spock follow him into the portal, despite Atoz's warning that they have not been "prepared". McCoy and Spock find themselves 5,000 years in the past, during Sarpeidon's last ice age. Exposed to brutal cold, they desperately search for Kirk.

Kirk has arrived in a different period, reminiscent of 17th century England. He rescues a disheveled woman being assaulted by armed men. Kirk chases the assailants away, but discovers that the woman is really a thief who was attempting to pickpocket the men. He offers McCoy's services for her wounds, but realizes that he is alone. Where the portal had been is now a blank stone wall. He can hear and speak to McCoy and Spock, but they are not physically present. Spock surmises that the planet's population has escaped destruction by migrating into the past. (Atoz later confirms this, and that he was preparing to leave when the landing party arrived.)

The local authorities arrest Kirk for helping the thief. McCoy asks Kirk to describe what is happening. The guards are shaken when they hear the disembodied voice. The thief betrays Kirk and accuses him of witchcraft, and claims that the voices are spirits who possessed her.

Spock and McCoy are rescued by a figure wrapped in heavy furs, who takes them to a warm cave. The figure disrobes as a beautiful woman, and introduces herself as Zarabeth. She explains that she and her family have been exiled there as punishment for their involvement in an assassination plot.

Kirk is interrogated by a timid, hypocritical prosecutor who loudly proclaims his belief in witches to anyone listening. Kirk suspects that he is a refugee from Sarpeidon's future. Kirk mentions the library and the Atavachron, and the prosecutor becomes nervous. The prosecutor believes that Kirk is innocent, but the guard and the thief maintain they heard the "mysterious" voices and that Kirk must be a witch. Kirk asks the prosecutor's assistance to return to the library, but the prosecutor becomes frightened and flees, exclaiming that he wants nothing more to do with the prisoner.

McCoy and Spock describe how they arrived in the past. Zarabeth confirms that she too is from Sarpeidon's future. She explains that passage through the Atavachron is one-way only and alters the molecular structure of the traveler. If they return to their original time, they will die.

Kirk overpowers his jailer. The prosecutor returns and Kirk threatens to expose him to the others as a witch if he does not help Kirk escape. The prosecutor warns Kirk that once "prepared", a body cannot return through the Atavachron. Kirk remembers Atoz's use of the word "prepared", and says that Atoz didn't prepare him. The prosecutor becomes alarmed, and warns Kirk that he must return to the library at once; an unprepared body can only survive a short time in the past. He guides Kirk to the alley, and Kirk finds the invisible portal by touch.

Kirk steps through the portal and confronts Atoz. Kirk demands Atoz help him rescue his friends. Atoz refuses to help until Kirk "prepares" himself. In desperation, Kirk tries to force Atoz to cooperate, but Atoz stuns Kirk with an energy weapon.

Spock slowly reverts to the barbarism of the ancient Vulcans living in that same time period. Spock becomes hostile to McCoy's playful insults. Spock falls in love with Zarabeth and announces he has no intention of returning to the future. McCoy is not convinced that they are trapped in the past, and accuses Zarabeth of lying to keep them there.

Kirk revives and overpowers Atoz. He forces Atoz to find the era where his friends are trapped. Atoz tries several disks until Kirk remembers that they were somewhere very cold. Kirk shouts through the portal. McCoy, Spock and Zarabeth have returned to their side of the portal, and respond to Kirk's cries. McCoy waits while Spock and Zarabeth share a tearful farewell; Zarabeth admits she would have done anything to keep Spock there, but proximity to the portal causes Spock to recover his normal personality and he explains that he cannot stay.

The landing party reunites in the library. Atoz snaps his data disk into a viewer and disappears through the portal. With only moments left before the planet is destroyed, the landing party returns to the Enterprise, which escapes the system just as the star explodes.[1]

Errors and Explanations

The Nitpicker's Guide for Classic Trekkers

Plot Oversights

  1. Zarabeth wearing a skimpy outfit in the caves. Perhaps the hot springs make the caves too warm for her to wear the full length fur robe.
  2. Spock tells Zarabeth that he comes from a place "millions" of light-years away. The Milky Way is approximately 100,000 light-years in diameter - so "millions" of light-years would place Vulcan well outside the galaxy (contrary to Star Trek canon). This may be a sign of the mental regression he suffers as a side-effect of time travel.[N 1]

Continuity and Production Problems

  1. When Spock and Zarabeth are talking, then Spock turns to see McCoy standing at the cave entrance, we hear McCoy say "You've been dishonest with me, Spock," but his lips don't move.McCoy could be a ventriloquist.[N 2]

Internet Move Database

Character error

  1. When Spock tries to use his phaser to warm a boulder at the base of the ice cliff, it doesn't work - presumably because phasers didn't exist in that time period. But when he lays McCoy out in Zarabeth's cave and examines him, the doctor's medical tricorder seems to work just fine.Perhaps Zor-kahn, the tyrant who exiled Zarabeth, arranged for the time portal to disable obvious weapons as part of the punishment, without harming other equipment.

Plot holes

  1. When the prosecutor is talking to Kirk, the mort (female thief) in the next cell accuses Kirk of being a witch. The constable confirms this, saying that Kirk talked to unseen spirits, one of which he called "Bones". Even though Kirk did address Dr. McCoy as Bones through the unseen time portal, the constable was not present when he did.[N 3] The constable could have been out of view but within earshot when Kirk called out to McCoy.

Fandom Contributions

Plot Holes

  1. User This episode is annoying due to fact that at time stamp 5:45 Captain Kirk failed to properly introduce themselves as they were from the Enterprise a Federation star ship. Of course, then there would have been no journeying off to any chosen past, as then Mr Atos would have understood that they do not belong there. My problem is that everything hinges off the fact that Captain Kirk did not introduce themselves as the catalyst and not something more substantial. I.e. remember when Dr. McKoy went back in time as he was not well at the time in different episode. this was more realistic scenario in my opinion. So why did they fail to do something more convincing as the catalyst and problem?? Maybe Kirk expected Atoz to instantly realise they did not belong there just by looking at their uniforms.

Continuity Errors

  1. User When Kirk goes through the portal he has his phaser. When he comes phaser. It was most likely confescated when he was arrested, and never returned.


  1. Listed under Character errors in the Internet Movie Database entry
  2. Listed under Audio/visual unsynchronised in the Internet Movie Database entry.
  3. Mentioned under Great Lines in the Classic Trek Nitpicker's Guide entry..


  1. All Our Yesterdays at Wikipedia

The Original Series Season 3
Spectre of the Gun I Elaan of Troyius I The Paradise Syndrome I The Enterprise Incident I And the Children Shall Lead I Spock's Brain I Is There in Truth No Beauty? I The Empath I The Tholian Web I For the World Is Hollow and I Have Touched the Sky I Day of the Dove I Plato's Stepchildren I Wink of an Eye I That Which Survives I Let That Be Your Last Battlefield I Whom Gods Destroy I The Mark of Gideon I The Lights of Zetar I The Cloud Minders I The Way to Eden I Requiem for Methuselah I The Savage Curtain I All Our Yesterdays I Turnabout Intruder