In a nutshell: an escaped prisoner holds seaQuest hostage by threatening to release a deadly virus on board.

Now this is an interesting episode. We start with Ford and Hitchcock travelling by launch to the remote prison under an ice cap, to collect the only prisoner remaining there, who is under such high security that they don't even know who it is. Why are Ford and Hitchcock on this duty? Hitchcock is the chief engineer, not a security officer. Surely they should have sent Crocker – what is the point of having a security chief if you don't make use of him for security matters? They arrive to complete confusion, and a man claiming to be the warden barges aboard pushing a cryogenic chamber containing his prisoner, and tells them that everyone else is dead and that the prison is on fire. To me, it was instantly obvious that the prisoner had switched places with the guard, but nobody questioned that he was who he claimed to be.

Back aboard seaQuest, the warden is made welcome, and the cryogenic chamber placed under guard – especially when they learn that the prisoner is Dr Rubin Zeller, convicted of crimes against humanity having experimented with biological weapons and murdered many people. While Bridger gives the warden a tour of the bridge, O'Neill is seen off-duty having lunch in the officer's mess with weapons officer Phillips. Phillips has seen the prisoner encased in his icy chamber, and jokes about it to O'Neill. This is a pretty nice little scene for O'Neill fans – seeing him off-duty and relaxing with a friend, although, of course, Phillips is only an Occasional Extra. Dr Westphalen is at a nearby table and overhears, reacting oddly to the prisoner's name. She rushes off.

Westphalen takes the warden on a tour of the boat, asking lots of questions about Zeller (and by now the viewer is screaming for someone to realise that the warden is a fake, and desperate to know why she is so fascinated by Zeller). Discovering a mutual fondness for chess, they agree to meet later for a game.

An REFS (Random Extra Female Scientist) sits herself down in the sea deck to munch on a sandwich in the gloom (why doesn't she put the light on? Oh, because that would spoil the spooky effect) and hears a dripping sound. Noticing that the cryogenic chamber appears to be switched off and defrosting, she goes over to investigate, sees blood dripping out of it, and raises the alarm.

It is, of course, quickly discovered that the corpse in the cryogenic chamber is in fact the warden, murdered by Zeller, who is now loose aboard the boat.

Chief Crocker discovers one of his RESLs (Random Extra Security Lads) laid out by the weapons room he was meant to be guarding, with several items missing.

Occasional Extra Dr. Levin (in his first appearance?) treats the RESL, since Westphalen is nowhere to be seen and apparently off-duty. Bridger orders a search of the boat and asks if all the crew are accounted for. All but one, apparently, but since this missing one is not named it is clearly nobody important. Oh, and Levin explains that Zeller has cut off the warden's fingertips and grafted the prints onto his own fingers; there is also a bizarre cavity cut in the warden's chest, which has got them all confused. It is all rather gruesome.

Meanwhile, Zeller is playing chess with Westphalen. They are getting along nicely, when Bridger, Crocker and some Security Lads burst in and arrest Zeller. He is amused by them, commenting that he expected them to get wise to him sooner. Westphalen is horrified to learn who he really is, and gets a comforting hug from Bridger. One for all the shippers out there.

Bridger gets Lucas to do some digging on Zeller.

Can't remember what happened next. I think it was Bridger and Ford going to see the restrained Zeller, who baits them. Ford loses his cool and lunges at the prisoner, going to throttle him, and has to be restrained himself. Ford really isn't the cool, calm and collected character that he is made out to be, that much is apparent even this early. Zeller tells them that he has created a virus that was concealed in the cavity in the warden's chest in a block of ice. Now that is has been removed from the cryogenic chamber and is hidden somewhere on the ship, the ice will start to melt – eventually the virus will be released and the crew will die.

Bridger calls a meeting of all department heads in the wardroom in 15 minutes. All department heads turns out to be Ford, Westphalen and Hitchcock. I would have thought there were more departments than that. Anyway, they agree that the virus has to be found, and that they can't risk contaminating the ocean. Bridger orders the boat's temperature to be reduced to rock bottom, to prevent the virus defrosting, and summons Krieg. He seems alarmed to be pulled into a meeting of this level, but Bridger has heard that he has invested in thermal underwear he was intending to sell to the crew for a profit (we had earlier seen Lucas discovering the scam and disapproving) and orders him to distribute them free – in exchange for not getting busted for bootlegging. A morose Krieg agrees. From this point on, we see everyone wearing their cold weather gear – thick woolly hoods and the like.

Erm, Bridger and Crocker are taking Zeller somewhere, I forget the details, when he manages to escape by triggering an electronic device he had set up earlier with stolen components, trapping them. Darwin the Genius Dolphin sets them free by splashing the device and short-circuiting it, but they have now got a psychopathic mass murderer loose on the boat. And Crocker finds the missing crewman in the hyperbaric chamber, shivering and unconscious. It escaped me just what the point of this was meant to be, other than further establishing Zeller's credentials as a Thoroughly Nasty Piece of Work, which we had already grasped.

Bridger goes to see what Lucas has found out, which isn't much. All records on Zeller have been erased, except one – a recording of his conviction. They learn he was convicted of the murders of a team of scientists working on a remote island, after he infected them with a virus he had devised. The party was led by a Dr James Westphalen … and although not much is made of this by them, the audience now knows why Kristin Westphalen was so interested. This was clearly a relative of some kind.

Bridger orders Lucas to stay in his room and out of sight and in safety, in a rather touching scene, even for me who doesn't like too much emphasis on the Bridger-Lucas surrogate-father-surrogate-son stuff. It kind of emphasises the danger that they are all in with this lunatic on board. It also emphasises the difficult position that Lucas's presence on board puts Bridger in: in times of crisis, having an underage civilian aboard can't be a good thing, as the responsibility is an unneeded distraction. And it's not as though Bridger ever agreed to take responsibility for Lucas, as the boy's presence on the boat had already been agreed to before Bridger took command.
Erm, on the bridge, Bridger orders the boat to find a nice deep trench to dive into, in order to minimise the environmental catastrophe should the virus be released. Then (I forget the exact sequence of events) he and Ford get shanghaied by Zeller, who is wielding the phial containing the virus. The two of them are herded into the weapons room and ordered to arm the nuclear weapons, using the special DNA coded keys that Zeller knows they both have. Bridger agrees, albeit reluctantly; Ford is absolutely horrified, and argues against it, but follows orders.

On the bridge, the sudden arming and aiming of their nuclear weapons causes great consternation. In the absence of Bridger and Ford, Hitchcock is in charge, and does a good job of ordering everyone around and trying to find out what is going on. Ortiz informs them that they are aiming at Pearl Harbour, which I suppose for an American audience is nicely symbolic but to a mere Brit just seems overly hysterical. On the other hand, since they always dry dock at Pearl maybe the target was chosen for strategic reasons rather than historical. Phillips is unable to override the command, and Lucas suggests that he try. Phillips doesn't look happy, but O'Neill convinces him to allow it. So Lucas isn't yet the automaric answer to all their problems. Also, this indicates that perhaps not all the crew are happy about having Lucas aboard, and who could really blame them. For military personnel, having a large science contingent aboard is bad enough, but add to that an unattached youngster with no real function aboard the ship – then having it suggested that this youngster knows more about their systems than they do is just adding insult to injury. However, Lucas also can't do anything (phew! The boy is still human). Meanwhile, Westphalen has slipped out of the room.

Back in the weapons room, the two prisoners turn their keys and fire the missiles (creating even more consternation and sheer disbelief on the bridge). They are then even more horrified when Zeller tells them that he lied, and tosses the virus phial into the air. Ford dives to catch it … and misses. It shatters right in front of him, in a truly wonderful scene, because everyone would be expecting the miracle catch. His face is a picture, as Bridger hauls him to his feet, as he clearly is expecting to expire on the spot from this virus. It doesn't happen. Zeller the gamesman laughs, telling them that it was all a ruse. Bridger promptly informs him that they decided to play him at his own game a long time ago – the warheads were disarmed and had their trackers fiddled with. Sure enough, on cue, the missiles crash and dive into the ocean, quite safely. Zeller is deflated. And I wanted to know just how many people were in on the ruse? Did Bridger do it alone? Certainly, no one on the bridge seemed to have the faintest idea what was going on. What about Ford? Was all his horrified protest just an act? Because if so, he missed his calling in life.

And at that moment, Westphalen arrives, gun in hand and bristling with grief and fury. Bridger and Ford are uneasy: she is a loose cannon, and they don't know what she will do and can't predict her actions. They try to talk her out of killing him, but she doesn't seem open to reason. She tells Zeller that he killed her brother, scientist James (and now the audience knows that Westphalen is her maiden name). Zeller doesn't seem to care, inviting her to shoot him. No, she says. She has a better idea. He isn't the only biochemist on board. She pulls a phial out of a pocket, flicking the cork out. For the first time, Zeller looks scared, realising that she is serious. She taunts him, reducing him to begging for his life, and then flicks the contents of the phial at him. He screams, hands flying to his face … and realises that it was only water.

'Checkmate', says a grim Westphalen.

Zeller is returned to the brig; the boat gets back to normal. Westphalen is shaken by the experience, revenge on her brother's murderer being anything but sweet. Bridger makes the supreme sacrifice of offering to play chess with her, only to be rebuffed as she no longer likes the game. But then she calls him back, offering a branch – perhaps he could teach her poker, instead …

And as a punishment, Krieg and Lucas have to collect, sort and wash all the thermal underwear – Krieg for attempted bootlegging, and Lucas for dobbing him in.

Overall, a pretty good episode. The 'stars' – Bridger, Westphalen and to a lesser extent Lucas – get a good work out, and are able to stretch their acting muscles. Less is seen of the rest of the crew, and almost exclusively at work. It was good to see how Hitchcock reacted to being in charge during such a crisis, and she rose to the occasion; in stark contrast, her ex-husband Krieg was pure comic relief. Ford also did well, in his difficult position of first officer to an unpredictable captain. Ortiz again demonstrates his importance on the bridge. The actor was only 23 here – the youngest bridge officer? Whatever, he is a key person on the bridge, and is 100% Mr Professional here.