1. Startled Deer
Aboard the HMS Goliath, a British stealth nuclear submarine, the crew are participating in a training exercise with the Americans. However, the mission goes wrong when live missiles are fired at a U.S. boat. Lieutenant Jack Trainor and Commander Alison Fairbanks bicker over who is responsible, and Jack believes that Captain Paul Wade is not actually a real captain, having known a Captain Peter Wade while in training. With a press pack onboard, the crew decide to stealthily slip away before releasing the press pack into a lifeboat. The crew submerge before resurfacing and coming under fire from Chinese pirates.
2. Special Relationship
The submarine finds itself off the coast of South Africa and has forty-eight hours of downtime, which allows some of the crew to enjoy the surface while others are stuck doing exercises. However, they receive orders to welcome aboard a team of U.S. Navy Seals who are to spend some time with them. Alison intends to enjoy the company of one of the Navy Seals to whom she has taken a fancy, while Jack wonders whether their visit will be a ticket for him to get away. Captain Wade arranges for the visit by having fish and a beachball delivered to the boat in anticipation of their guests.
3. Prize Hamper
Just off the coast of mainland Russia in the Arctic, HMS Goliath has received new orders that the admiral will be coming aboard, though Jack's opinion of the man is one word: idiot. The admiral arrives though mistakenly lands himself on a Russian submarine, which leads to a number of British officers needing to launch a mission to rescue the admiral. However, Jack finds himself out of favour with the admiral when he challenges the admiral's declaration of a "fun day". He also finds himself in trouble again when the admiral's wife makes a pass at him, until she finally stands up for herself.
4. Crispy Duck
In the North Atlantic between Iceland and Greenland, Jack is playing hide-and-seek though the rest of the crew take to drinking instead. The upcoming end-of-tour party has everyone distracted, which results in Jack sending the submarine coordinates unencrypted for the return home. The boat is also requested to pick up "Crispy Duck" on the way home, who turns out to be astronaut Minty Fowler. Jack finds that Minty claims he was visited by aliens, while the Royal Air Force doesn't want him back. Jack's attempts to convince everyone that Fowler is a spy ends with him going seemingly mad.
HMS Goliath prepares to set sail again with some new faces including Alice "Barry" Barry, who has a distinct lack of excitement. Alison announces that she is leaving when they make a stopover in Naples, due to a lack of appreciation, as she has a job with NATO. A delighted Jack has the job of showing Barry around the boat, and gets to meet the new catering manager Diana who completely changes the menu. Jack also has to cope with changes when a replacement for Alison is due to arrive, and sets about putting a plan into action using Barry, and swapping Diana for Alison when they stop off in Italy.
2. Old Friends
In Norway, Captain Wade, Jack, Alison and Barry are attending a submarine expo, where Alison meets a French navy member, Philippe, but unfortunately misses out on getting his phone number. After the event, she tries to get the number from Barry, while Jack meanwhile has been extra cranky. He eventually reveals his friend, Daniel, has died who turns out to be a Spaniel dog. Jack's only other friend Major Sam Baker arrives on the sub, though he finds that he is now a she, which he takes badly. However, it takes Barry saving her life to remind Jack of his friendship though she takes to celebrating by sleeping with Wade, leaving Alison jealous.
3. Nuclear Reactor
In the Pacific Ocean, HMS Goliath is working to battle the international drug trade. However, their mission is affected by a cooling leak from the nuclear reactor, though Jack is confident he can fix the issue. Quickly making the issue worse, the crew have to take refuge on in an area of South America where drug trafficking is rife, leaving them having to avoid trouble. Jack again quickly gets in trouble by losing at poker, and finds himself imprisoned alongside Alison. Escaping, and eventually meeting up with Wade and Barry who also meet their own problems, they head back to the submarine to handle the repairs.
4. End of the Voyage
Christmas time is approaching and the submarine is located in the north Atlantic, and after six months at sea, it is heading back to Portsmouth. Jack is having problems printing his nativity play script for the end of tour show they are all taking part in, which includes a range of surprising props. Captain Wade meanwhile is looking for Christmas guests to attend dinner at his home. Jack meanwhile has plans for receiving a motorbike for Christmas which is being delivered quayside when they dock. Everyone also meets Barry's flatmate - Daniel Craig - while Jack's bike arrives to much disappointment.