An unusual take on time travel: instead of traveling to Earth's past, the main trio get stuck in the past history of another planet. They beam down to this planet, whose sun is scheduled to go nova in 3 or 4 hours (that's cutting it close!). In some kind of futuristic library, they meet Mr. Atoz (A to Z, get it? ha-ha) and his duplicates. It turns out, instead of escaping their planet's destruction via space travel, the usual way, the inhabitants have all escaped into their planet's various past time eras. Mr. Atoz uses a time machine to send people on their way after they make a selection (check out the discs we see here, another Trek prognostication of CDs and DVDs!). When Mr. Atoz prepares the machine (the Atavachron-what-sis), gallant Kirk hears a woman's scream and runs into the planet's version of Earth's 17th century, where he gets into a sword fight and is arrested for witchery. There's an eccentric but good performance here by the actress playing a female of ill repute in this time, using phrasing of the time ("...you're a bully fine coo.. Witch! Witch! They'll burn ye...!"). Spock & McCoy follow Kirk, but end up in an ice age, 5000 years earlier.<br /><br />Kirk manages to get back to the library first. The real story here is Spock's reversion to the barbaric tendencies of his ancestors, the warlike Vulcans of 5000 years ago. This doesn't really make sense, except that maybe this time machine is responsible for the change (even so, Spock & McCoy weren't 'prepared' by Atoz - oh, well; it also seems to me Spock was affected by the transition almost immediately - he mentions being from 'millions of light years' away, instead of the correct hundreds or thousands - a gross error for a logical Vulcan). In any case, Spock really shows his nasty side here - forget "Day of the Dove" and remember "This Side of Paradise" - McCoy quickly finds out that his Vulcan buddy will not stand for any of his usual baiting and nearly gets his face rearranged. Spock also gets it on with Zarabeth, a comely female who had been exiled to this cold past as punishment (a couple of Trek novels were written about Spock's son, the result of this union). All these scenes are eye-openers, a reminder of just how much Spock conceals or holds in. It's also ironic that, only a few episodes earlier ("Requiem for Methuselah"), McCoy was pointing out to Spock how he would never know the pain of love - and now all this happens. Kirk, meanwhile, tussles with the elderly Atoz, who insists that Kirk head back to some past era ("You are evidently a suicidal maniac" - great stuff from actor Wolfe, last seen in "Bread and Circuses"). It all works out in the end, but, like I mentioned earlier, they cut it very close. A neat little Trek adventure, with a definite cosmic slant.