In the year 2151, the Wendover class starship HMS Camden Lock travels the stars, protecting and promoting British interests in the wider universe.
Captain Michael Henderson (aka "Mike", "Lucky Jack", "Hendo") and diplomatic officer Chloe Teal welcome representatives of the Glish on board (after he stops his weapons officer from firing missiles at their approaching ship) in order to conduct trade negotiations, with a view to the Glish setting up businesses in the Peterborough area.
Unfortunately though, the Glish are a repulsive species, whose various bodily orifices exude a disgusting mucus, and whose greeting ritual includes having them lick the hands of those whom they are meeting with.
The trade negotiations seem to go well though, regardless of this, however when a deal is about to be struck., the Glish announce that it is their tradition to lick the face of one of the representatives, which ends up being Officer Teal. Captain Henderson starts off being relieved that he didn't have to endure this, but then causes a diplomatic fall out by refusing to partake in the other part of the ritual, which would call for the Glish to rub their genitals on his face. It is also at the same time that the Glish admit that they have no interest in doing business with the British government, and instead are just killing time until they go to meet the Americans, and, as a big "fuck you" parting gift, they leave a small, but deadly, carnivorous parasitic creature on board the Camden Lock.
Hendersons superior is obvioulsy unhappy that the trade deal wasnt set up, and reminds Henderson that the captain of the space ship which shuttles school children on day trips to the moon (otherwise known as "The Brat Run") will soon be needing a new captain, as the current one is due to take early retirement due to stress.
Henderson quickly reviews all the available alien planets to find someone who would be willing to broker some sort of trade deal. Most of them are dismissed due to already setting up deals with other countrires, however Henderson finds that the planet Uberon hasn't yet set up any deals with anyone, mainly because they are isolationist and highly xenophobic, so, he orders the ships navigation officer to set course for Uberon at maximum speed, which he is unable to do, being as he has spilled coffee on the navigational computer (an accident engineered by the ships technical officer to prove the point about why drinks are not allowed on the flight deck), rendering it inoperative.
Hendo orders the computer repaired as soon as possible, however just then the ships paranoid and highly sociopathic weapons officer, Eduardo York, reports that the Glish creature has begun killing crew members, starting with the ships guinea pig. Hendo orders the creature to be hunted down and killed before they get to Uberon, a task which York relishes.
Henderson, getting bored by chief engineers Jeffers constant insistence of doing the repair job properly, over rules him and simply restarts the ships computer to factory settings, which although fixing the problem with the navigation system, causes other problems, such as making the ships toilets insisting that people wanting to use them input digits from their ridiculously long PIN numbers, and resetting the ships small arms to require a lengthy health and safety questionnaire to be completed before they will actually fire (The subject of health and safety concerns is a running gag throughout the series).
The ship finally arrives at the planet Uberon, where Henderson is contacted by Fasmoff, a representative of their government, who promptly tells him to bugger off. As Henderson launches into an impassioned speech to try and get to speak to someone about setting up a trad emission in Peterborough, but Fasmoff has no interest in speaking to him until he spots Chloe Teal in the background, and remembers her from his University days. After a brief bit of banter, Fasmoff says he will come aboard the Camden Lock to meet with Teal to reminisce.
When Fasmoff arrives, York still hasn't caught the alien parasite, so Hendo orders that it be caught quickly before Fasmoff notices it, but by this time, the creature has graduated on to killing actual crew members, starting with the "slowest", and York is relishing in the big game hunt, causing further problems as his over indulgence in the spirit of the hunt causes him to miss several good opportunities to capture or kill it.
Over thecourse of their talks, Fasmoff says he realises that a political shift at home will soon bring an end to his species isolationist stance, and that trade with Britain would be a good idea, but, Peterborough would be too small for their needs, so he would require Ealing, Doncaster and the entirety of Wales as well, Hendo agrees, just to get him to sign the trade agreement, but as they enter the conference room, he notices a severed leg on the table, so hurriedly escorts Fasmoff to "meeting room 2", which is in fact the ships urine reprocessing room, all while assuring Fasmoff he is perfectly safe.
Angry that York hasn't killed the creature, Hendo and Teal leave Fasmoff in the urine reprocessing room and grab some weapons to join the hunt, but Fasmoff, knowing that something is wrong, radios for pickup and heads to the nearest air lock, where he is attacked by the creature.
Hendo, Teal and York save him, but as they try to kill it, the creature attacks Jeffers, and their weapons insist on a long health and safety questionnaire being completed before they will fire. Eventually, Fasmoff kills the creature with his own gun, which is hardly bigger than a small dog, and insists on returning home in a state of shock, and not being really interested in trading with Britain after the days problems.
Hendo, understandably angry about the prospect of being captain of the Brat Run, orders Teal to do whatever she can to get a trade deal signed, so she resorts to cold calling random planets to try and sell the deal, which results in the whale people swearing at her as they hang up.