The first summary was released on Watch's website. When a nuclear submarine encounters an anomaly and Liopleurodon in the sea, the team are called aboard to help. They soon find themselves under attack once more, and get sucked back through an anomaly, with Liopleurodons damaging the outside of the sub. The team must not only capture the panicked Eustreptospondylus aboard, but fix the sub exterior in order to get home.
The second summary was released in a promotional book distributed to select people who were helping promote the show. When a nuclear submarine encounters an anomaly and a Liopleurodon in the sea, the team are called aboard to help. They soon find themselves under attack once more, and get sucked back through an anomaly, with Liopleurodons damaging the outside of the sub. The team must not only capture the panicked Eustreptospondylus aboard, but fix the sub exterior in order to get home. Meanwhile at the ARC, Lester has to cope with the intervention of Navy bigwigs, threatening to nuke the sub if the team can't fix the problem. The political fallout from any damage caused by the anomaly is too big to ignore. Jess and Lester are working against the clock as they attempt to distract the Admiral long enough for the team to do its stuff.
A british nuclear submarine cruises the North Sea. As they continue on, the captain is alerted when the submarine encounters electrical failure. The submarine then picks up animalistic sounds in the water and the captain orders the submarine to surface. As it goes up, an anomaly can be seen as the reason why it caused electrical problems. From out of the darkness a massive figure swims towards the camera- a massive marine reptile!
At the ARC, Matt questions Abby as to possible reasons why Philip purchased certain items. Abby suggests they just talk to Connor but Matt thinks this is a bad idea. As an anomaly alert goes off, Abby reveals that she did some research and learned of what happened to Emily after she returned to her home however Matt doesn't want to know. As Abby reaches Connor's lab she tells him of the anomaly and also comments on how he seems less caring of anomalies these days and more on his work for Philip. Connor apologizes and promises to be more alert with new anomalies. The team arrive at the anomaly detector and learn that the anomaly is smack bang in the middle of the North Sea. Lester then gets a call from the Admiralty reporting that a creature was found on the bridge of their submarine.
The team arrive at the docks and are escorted by the captain who doesn't appear the least bit impressed with the ARC team. He seems reluctant to let their locking device on board however Matt claims that its "scientific equipment". The team arrive on board the submarine and Abby is escorted away to look at the creature being held in the cargo hold. The captain tells Matt and Connor that due to the secretiveness of this mission that he is only permitted 3 crewmen- something he is not happy about.
Abby arrives to find the creature is a theropod- a juvenile, female theropod. Abby theorises that this species's must have been able to swim and got sucked through the anomaly however the crewman appears confused about her talk of anomalies. Abby realizes to her surprise that the swimming black raptor-like creature is still alive and in order to keep her in a state of shock, they lock the creature in a freezer.
Connor and Matt meanwhile put the special under-water locking device together. By placing an anomaly locking device in a torpedo, they can shoot it right through the anomaly which will lock it as it passes through. Connor also apologizes to Matt that he hasn't been as alert with dealing with new anomalies these days and that his work with Philip is "new and exciting". Matt decides to use this as a moment to ask Connor what this work is but Abby interrupts them. The team then retire to their cabins as it is at least another hour to the anomaly.
At the ARC, Admiral Marston arrives to observe the team. He appears skeptical of the team's effectiveness.
As the submarine nears the anomaly electrical interference begins to wreak havoc on the submarine- suddenly, something massive grabs the submarine's GPS tracker and slings it around the propellar jamming it and causing the submarine to lose control of steering. Suddenly, the submarine suffers a blackout. The captain is thrown agaisnt a wall and is knocked out in the process.
Meanwhile, one of the crewmen- Officer Neal- who was fetching coffee while this was happening winds up near the freezer, its electrical locks no longer effective. Hearing strange noises he slowly creeps towards it and is spooked when the door suddnely flies open. Suddenly, the swimming theropod leaps out of the freezer and with a great roar- Neal is no more.
Matt, Connor and Abby arrive to see what has happened. Matt orders that Officer Shaw find Officer Neal, Connor find the fuseboxes to restore power and he and Abby will use the Bathyscope to untange the GPS from the propellor.
At the ARC, Lester, Jess and the Admiral are horrified to see what is going on. With no power, the submarine is just floating... right towards the anomaly! On board the submarine, the team have realized the same thing and brace themselves as they are sucked right through... unbeknowst to them, followed by a massive marine reptile....
As the submarine arrives on the other side of the anomaly- speculated to be the Jurrasic- Officer Sam becomes worried and realizes who the ARC team really are. Connor tries to correct Sam's notion about where in time the Jurrasic really is but Matt tells Connor that this is no time for an Earth's history lesson.
Admiral Marston meanwhile is beginning to get annoyed and tells his assistant to position the HMS Frost to get into position and move the Vanguard into position. Upon realizing that this is a nuclear class submarine, Lester and Jess realize that the Admiral intends to nuke the anomaly!
As Officer Shaw makes his way towards where Officer Neal was, he finds a mess everywhere- and Officer Neal's remains! Suddenly a loud roar can be heard and Officer Shaw's screams can be heard echoing across the halls. Connor hears them and realizes that the theropod is on the loose!
Abby and Matt drive the Bathyscope towards the propellor where they begin to untangle the wires from the propellor. As they do it, something scrapes against the top of the machine. Matt and Abby suddenly realize what it is. A Pliosaur. They soon realize that not just one, but a whole pod of them are swimming right towards them. Matt instructs Abby to turn off the lights and "play dead". Sure enough it works and the Pliosaurs lose interest in the Bathyscope. They then untangle the wire and return to the submarine.
At the ARC, Admiral Marston explains that the North Sea is the busiest submarine vector on the face of the planet. He says that the United States, China and Russia all have submarines deployed in those waters and if one of their submarines were to dissapear off the coast of Britain- it could start World War 3. Lester goes off to call the minister.
Connor meanwhile has managed to locate and fix all but one of the fuse boxes. As he searches he runs into Abby who is searching for the theropod. They find the last box and fix it and are startled when the theropod finds them. It roars and attacks but Connor knocks it out with an electrical shock. The theropod is then taken to the torpedo room where Matt intends to shoot it out of the submarine.
With power restored, the submarine is moving back through the anomaly. With the Pliosaurs slamming into the outside however, the submarine begins leaking! In order to distract them, Matt fire the theropod out of the torepedo bay where it is quickly devoured by the Pliosaurs.
With the minister agreeing with the Admiral, Lester realizes that there is no other option. With a prehistoric era about to be nuked, he realizes that the world is going to be very different with this cataclismic event in the earth's timeline. The nuclear torpedo is fired off.
However, just as the torpedo is launched, the submarine comes back through the anomaly! The Admiral quickly tries to abort the order but it is to late- the torpedo is heading right for the submarine!
On board, the torpedo is detected and the team and Sam just manage to steer clear of it and fire off their torpedo which locks it as it passes through.
The Admiral is relieved however not so relieved when he receives a call from the Prime Minister himself who chews him out much to the entertainment of Lester and Jess.
Back on shore, Matt notices a saddened Abby watching Connor on the phone with Philip. She tells Matt that with the two of them dealing with an anomaly, it was just like old times.
Abby later confronts Connor in his lab and tells him that Philip is not who he seems to be and that he is dangerous. Connor however tells Abby that he believes that Philip is a good man and that when his work is over, that she will be proud of him. But a teary eyed Abby tells Connor that she was already proud of him.
Abby later finds Matt and tells him that its important he know what happened to Emily as she knows that Matt misses her. Abby had caught Matt longingly twirling her dagger which he carries with him. Matt sighs and realizes that she is right and opens up the envelope to find a newspaper article. Alongside the head article that a killer is on the loose named "Spring-Heeled Jack" is an article that- much to Matt's horror and sadness- reveals that Emily has been locked away in Bedlam Asylum.
- Ciarán McMenamin as Matt Anderson
- Andrew-Lee Potts as Connor Temple
- Hannah Spearritt as Abby Maitland
- Ben Miller as James Lester
- Ruth Kearney as Jess Parker
- Bosco Hogan as Admiral Marston
- Allen Leech as Officer Sam Leonard
- Tom O’Suilleabhain as Captain Marcus Yates
- Sam Peter Corry as "Submariner"
- Tony Kelly as Officer Shaw (uncredited)
- Jacqui Carroll as Cerise (uncredited)
- Matt Anderson
- Connor Temple
- Abby Maitland
- James Lester
- Jess Parker
- April Leonard
- Navy Admiral (only appearance)
- Sam Leonard (only appearance)
- Marcus Yates (only appearance)
- "Submariner" (only appearance)
- Shaw (only appearance)
- Philip Burton (mentioned)
- Emily Merchant (mentioned, picture)
- Anomaly Research Centre
- North Sea (only appearance)
- Jurassic Sea (only appearance)
- HMS Gartside (only appearance)
Objects and technology
- Anomaly Detection Device
- Anomaly Locking Mechanism
- Anomaly Locking Torpedo (only appearance)
- Biometric I.D. Tag
- Black Box
- HMS Gartside (only appearance)
- Bathyscaphe (only appearance)
- HMS Frost (only appearance)
- K-T Extinction (mentioned)
- In this Episode, while searching for the fusebox Connor said "I'm finding it, I'm finding it", previously while searching for Rex, whom he lost, he said "I'm finding him, I'm finding him" in Episode 1.5.
- In the DVD release of Series 5, this episode includes an additional scene not in the original British broadcast version: Whilst on board the HMS Gartside, Abby noticed that Matt was twirling a dagger and staring at it longingly. Abby realised that it was Emily's. When asked where he got it, Matt replied that it was evidence taken from Patrick Quinn's flat.