The next-to-last episode aired of the original Star Trek series is an interesting, sometimes melancholy installment that proves the show was still exploring its characters even at this point in the third season; though flawed, 'All Our Yesterdays' has its moments and overall a moody, compelling feel to it. Kirk, Spock, and McCoy beam down to a planet, assuming they are arriving in the nick of time to save or at least give some warning to whatever populace is there, since the planet's sun is due to explode within hours. But as it turns out, the people there are all too aware of the planet's fate, and using a kind of time travel device, have escaped into the past. Each person has been able to choose the time and place in the past where he or she would like to live at a 'library,' run by an elderly man named Mr. Atoz. Atoz assumes the three men are looking for a past to live in as well, and shows them various periods from which they can choose on viewers. There is some rather forced confusion at the start of the episode, with lines like:<br /><br />McCoy- Where did they go? Atoz- Wherever they wanted to.<br /><br />The misunderstanding could be cleared up rather easily, but for plot purposes, it isn't, and soon Kirk finds himself transported back to a period resembling 18th Century England, while Spock and McCoy are sent to an ice age, 5000 years in the planet's past. From here, the main focus is on Spock and his relationship with a woman exiled to this time by a tyrant as punishment. Spock begins acting increasingly emotional, showing anger toward McCoy and deep affection for Zarabeth, the woman. He eventually realizes that he is reverting back to the primitive emotional state of his ancestors on Vulcan, 5000 years ago. Kirk makes his way back to the library first, and finally convinces Mr. Atoz they don't belong in his planet's history. Spock and McCoy return just before it's too late, leaving Zarabeth behind; the Enterprise beams the three up and speeds away as the sun explodes, destroying the planet. The interaction between Spock and Zarabeth provides this episode's most memorable moments, though Kirk's adventure into the 'English' past is amusing. All in all, a very decent latter-day Star Trek outing.