10. Chain of Command, parts 1 & 2 (The Next Generation)
"There are four lights..." Haunting words for Next Gen fans. This two-parter sees Picard, Worf, and Beverly go undercover to take out a Cardassian weapons facility, while the Enterprise comes under the command of Ronny Cox's Captain Jellico. The mission goes awry, however, and Picard falls into the hands of the Cardassians who proceed to torture him for information. David Warner (at this point a Star Trek stalwart having appeared in both The Final Frontier and The Undiscovered Country excels as Picard's tormentor Gul Madred, and this haunting story plays out as Trek's take on 1984.
9. Darmok (The Next Generation)
The tale of Picard and a member of the mysterious, inscrutable Tamarian race forced to work together in order to survive is a brilliant exploration of language and the way it can be misunderstood. Darmok and Jalad at Tanagra has since become of the most quoted lines in Trek history. The episode took two years to come to fruition, and it was well worth the wait - this is Star Trek at its intelligent best.
8. The Devil in the Dark (Star Trek)
A classic Trek morality play. The Enterprise is despatched to a mining colony on Janus VI to investigate some deaths and encounters the Horta, a mysterious silicon-based lifeform. They attempt to kill the creature, only to discover that it means them no harm, and - as the last of its species - is simply trying to protect its eggs. It's a moving and funny episode, and contains the classic McCoy line, "By golly Jim, I'm beginning to think I can cure a rainy day!"
7. The Inner Light (The Next Generation)
This is Star Trek as proper science fiction, with a great central concept. Picard gets zapped with an alien ray and, in that brief moment, experiences 40 years as Kamin, a scientist on another world. Patrick Stewart gets some of his best ever material here, but a lot of the episode's beauty is down to its sheer sense of scale and the emotional punch when you realise that Kamin and his people are all long dead. The episode was so well regarded, it won a Hugo award - and rightly so.
6. In the Pale Moonlight (Deep Space Nine)
Deep Space Nine was characterised by its often bleak look at the cost of warfare. That's never more true than with In The Pale Moonlight, with the cost here being Sisko's soul. The war against the Dominion is dragging on, costing countless lives, so Sisko forms an unholy alliance with Cardassian spy Garak to help bring the Romulans over to their side. Garak's plan, however, involves a carefully targeted assassination - something that Sisko is furious about, but ultimately able to live with for the greater good. This is where Deep Space Nine excelled. Kirk and Picard would not have made the same morally murky choices that Sisko does here. It's Trek at its most surprising and brave.
5. Balance of Terror (Star Trek)
The episode that introduced the Romulans adds a huge amount to Star Trek lore. A long time ago, Earth fought a space war against this mysterious race. No human or Romulan ever came face to face so, consequently, the Federation have no idea that their enemy are, in fact, an offshoot of the Vulcan people. This is a brilliantly tense episode that pits Kirk against Mark Lenard's (who would later play Spock's pa, Sarek) nameless Romulan commander. As he points out towards the end, he and Kirk may have called each other "friend" in another life, but in this one they're merely soldiers in a galactic cold war.
4. Yesterday's Enterprise (The Next Generation)
Poor old Tasha Yar met an ignominious death in the season one episode "Skin Of Evil". Yesterday's Enterprise, however, finds a way to get Denise Crosby back on the show without betraying that earlier episode's punch. Time is rewritten when the long-lost Enterprise-C emerges from a rift in space and time. In this new reality, the Federation is at war with the Klingons, and Starfleet has become a much more militaristic outfit. It's down to Guinan to figure out what's wrong. The story for Yesterday's Enterprise was actually inspired by an unsolicited script sent in by a fan, Trent Christopher Ganino. While the script itself was not useable, the story was considered intriguing and subsequently bought from Ganino. It was a wise choice; Yesterday's Enterprise is a dark and daring episode that plays mainly to long-term fans, but in interesting ways. Peeking into a nook in Star Trek mythology is fun, and it's great to see Cosby back, if only briefly.
3. Far Beyond the Stars (Deep Space Nine)
Better than In The Pale Moonlight? We think so. Far Beyond The Stars is an unsubtle, but powerful allegory. A vision from the Prophets shows Sisko a world where he is Benny Russell, a down-on-his-luck science fiction writer in the 1950s. It's a story that cleverly weaves in aspects of Star Trek's own behind-the-scenes lore. With the regular cast playing different parts in Sisko's vision, Kira becomes Kay Eaton, a writer who is forced to use her initials to hide the fact that she's a woman from her conservative readership, while Sisko himself struggles with the racist attitudes of those around him. It's Avery Brooks' finest performance in the show, allowing him to be both commanding and cowed by the real life problems that surround him.
2. The Best of Both Worlds, parts 1 & 2 (The Next Generation)
This two-parter was a gamechanger, and not just for The Next Generation. Season 3's finale sees Captain Picard kidnapped by the Borg and converted into one of their own, ending on a jaw-dropping cliffhanger that would provide the template for genre show season finales for years to come. It's not just about the ending, though. Right from the off, there's something different about this story; the mood is dark and ominous, and there's a real sense that, in the Borg, the Federation have met their ultimate nemesis. It was the moment that, after three years of gradual improvement, The Next Generation finally became the show that it should be, and remains its best story.
1. The City on the Edge of Forever (Star Trek)
Everyone has seen this one, right? (If you haven't, go rectify that right now. It's okay, I'll wait). Star Trek's most legendary episode - written by science fiction guru Harlan Ellison - is both a real sci-fi classic, and a hell of a love story. Joan Collins guest stars as Edith Keeler, a woman that Kirk falls wildly in love with when the crew are transported to New York in the 1930s. One problem, though: history has been changed by their presence, and for reality to be restored, Edith must die. Kirk was such a ladies man that seeing him fall properly in love is genuinely affecting, and the ending is properly tragic.