Prisoners of the Lake (audio story)

Prisoners of the Lake was the first story in the audio anthology The Third Doctor Adventures, produced by Big Finish Productions. It was written by Justin Richards and introduced Tim Treloar as the Third Doctor, as well as the box set's narrator, and also starred Katy Manning as Jo Grant and Richard Franklin as Mike Yates.

Publisher's summary
Captain Mike Yates is investigating the disappearance of artefacts from an archaeological site deep below Dunstanton Lake. It's hardly a job for UNIT. But when the team discover a mysterious ancient structure buried deep underwater, all that changes.

When chief archaeologist Freda Mattingly ventures inside, she soon realises that her skills do not begin to equip her to deal with what she finds. As an ancient menace begins to stir the Doctor, Jo Grant and Mike Yates must dive down to the lake bed and discover the secrets hidden there. Secrets that could mean the end of all life on Earth...

Part one
At Dunstanton Lake, Director Pennard insists that the missing artefacts that UNIT has sent Captain Yates to investigate have simply been miscatalogued and were not stolen. Lead archaeologist Professor Freda Mattingly tells Yates that a building at the bottom of the lake and that the divers are installing an airlock in its door to get in. Freda explains that the building, or whatever it is, must date back centuries to when the lake was dry land.

Freda goes through the airlock and enters the structure, noticing that the rocks are fluorescent and that she does not need her torch. When Freda tries to communicate with Repford at Dive Control and he does not respond, she guesses that the rocks could be interfering with the signal and starts to make a sound record to show when she returns. She finds a blocky statue which moves and speaks, assimilating her language; it identifies itself as Defence Advocate 997 and apologises for its delay before becoming a statue once more.

The Brigadier receives Yates's report from a UNIT operative and passes it onto the Doctor, who shows no interest. Jo eventually manages to pique his interest by reading a transcript of what the statue said and they head off in Bessie to investigate, although Pennard is less than enthusiastic about them involving themselves. In the interest of maintaining a cordial relationship, Yates goes to speak with Pennard after the Doctor offends him.

The Doctor and Jo descend into the lake and Repford connects the access tunnel between the diving lift and underwater structure using the Ex-Cav suit, which briefly malfunctions but manages the task. The Doctor determines that the structure is a spaceship and that the statue is a degraded robot. His inspection is interrupted by the collapse of a wall and the death of Jeff, although he has been strangled rather than crushed. More wall collapses and another stone robot emerges, preparing to execute them.

Part two
The Doctor leads the slow-moving statue away and fights it with his Venusian aikido whilst Jo and Freda get the other archaeologists to safety. When he returns to the airlock, however, he finds Jo and Freda unaccounted for and joins the archaeologists in the safety of the airlock before contacting them with a radio. They tell him that they took a wrong turn and that he should get the archaeologists to the surface before returning for them.

Repford is having further trouble with his Ex-Cav suit and cannot get it to reattach the tunnel, so Yates send divers to complete the task. As the divers work, Jo and Freda go towards the airlock and see the statue standing there, unmoving until it detects their presence and declares that it will execute them. The Doctor, upon arriving on the surface, learns from Yates that the theft of the artefacts must be an inside job, the records having been deleted, and dives to connect the air tunnel for Jo and Freda. Repford is in the way, however, and the Doctor uses his sonic screwdriver to put the suit into standby.

As more oxygen is arranged to be taken down to Repford, the Doctor and Yates listen to Freda's recording and find that they cannot hear the statue despite Yates having previously been able to transcribe the conversation. The Doctor surmises that the statue's intelligence was stored on the recording but was transferred into the Ex-Cav suit when Freda rewound it.

Jo and Freda find themselves in an unexplored area and come across about thirty stone coffins with frosted glass lids with lupine aliens within. A video shows the destruction of cities and planets by the same creatures lying in the coffins. The Doctor dives into the lake and communicates with Jo and Freda, telling them to get to the airlock, but they are interrupted by the roar of the statue. The Doctor loses contact with them.

Part three
The Doctor enters the ship and finds Jo and Freda, who tell him about the passengers in suspended animation and the supposed newsreel. He orders the statue to stop and, after telling it that they came only to investigate the crashed ship, learns that the passengers are the Dastron military leaders and are being taken to stand trial for war crimes during an attempted invasion. This statue is the Prosecutor and the other, which has run out of power, is the Defender and will seek to release the prisoners now that the Jurisdictory is likely no longer in existence. The key to free them is one of the artefacts which has gone missing.

Yates informs Pennard that Inspector Hazeldine has recovered some of the missing artefacts from antiques dealer Alec Melshen, whom Yates knows that Pennard recently visited and regularly pays. Pennard pulls out a gun and admits to the crime before locking Yates in his office and leaving to make his escape, but Repford in his Ex-Cav suit stands in his way and, after Pennard shoots the suit, he chokes him and demands to know where the Revival Key is. Yates, having broken out of the office, brings Repford to his senses, but the suit remains in control and kills Pennard before going to his office.

The Doctor, Jo and Freda discuss how UNIT will have to close off the lake and spot Repford approaching them in the Ex-Cav suit, followed by Yates and carrying the Revival Key. They struggle with the suit, which falls into the water with the key and goes to free the Dastrons. Diving into the lake with Jo and Yates, the Doctor walks Repford through how to shut down the suit, but it opens itself in a bid to drown him. The suit continues its descent whilst Jo takes Repford back to the surface, sharing her oxygen with him and planning on calling the Brigadier.

Once the Ex-Cav suit has entered the ship, the Doctor and Yates follow it through the airlock. Using his sonic screwdriver, the Doctor begins the Prosecutor's reactivation process with his screwdriver and tries to stop the revival of the Dastrons. They try to flee back to the exit, but a Dastron stands in their way and growls.

Part four
Whilst Yates returns to the airlock to contact the surface, the Doctor fends off the Dastron with his Venusian aikido and tries unsuccessfully to convince him to return to suspended animation until the ship can be removed from the lake, after which they will be tried. Yates updates Jo, Freda and Repford before returning to help the Doctor, joined by the reactivated Prosecutor. Given the severity of the situation, Freda and Repford believe that UNIT should destroy the ship to prevent the Dastrons' escape.

The Doctor and the Dastron assess the condition of the ship and the likelihood of it getting them out of the lake, a task which would require the assistance of the Ex-Cav suit and the activation of the hyperdrive within the Earth's atmosphere, causing the deaths of millions. The Doctor manages to get away and sends the Prosecutor to fight the Ex-Cav suit whilst he and Yates try to extend the hibernation field to return the Dastrons to their slumber. The Dastrons fight back, however, and the Doctor and Yates lose hope.

Lieutenant Macintyre arrives at Dunstanton Lake with his platoon and agrees that the ship will have to be destroyed if the Doctor does not contact them in ten minutes. After the time elapses, Macintyre heads down into the water with his men and Jo, who refuses to be left behind.

The Prosecutor is knocked down and Yates places a grenade inside of the Ex-Cav suit just before it leaves through the airlock, blasting it to pieces in the water and causing a small amount of damage to the ship's wall. Yates hurries to tell the Doctor about the imminent flooding; the Doctor warns the Dastrons about the water and the damage that it will do to the hyperdrive systems, but they do not listen and begin the ignition. The water bursts in and the ship is destroyed when the systems are activated, but not before Jo and Macintyre are able to save the Doctor and Yates.

Cast

 * Narrator / The Doctor - Tim Treloar
 * Jo Grant - Katy Manning
 * Mike Yates - Richard Franklin
 * Freda Mattingly - Carolyn Seymour
 * Johnny Repford / Director Pennard / Statue / The Prosecutor - Robbie Stevens
 * Chief Dastron / Lieutenant Macintyre / UNIT Operative / Archaeologist - John Banks

Worldbuilding

 * Jeff is one of the archaeologists at the dig.
 * Yates is contacted by Inspector Hazeldine, who works at Rompchester Police Station. He tells him that some of the artefacts are being sold by Alec Melshen, a "dodgy dealer".
 * Repford uses the Ex-Cav suit.
 * The structure is lit by Vintaric crystals.
 * Dastrons are a murderous and expansionist race.
 * The Doctor dissuades Mike from using his gun, as he abhors violence.
 * Jo went on an underwater assault course the previous year.
 * The Doctor uses Venusian aikido against a Dastron.
 * UNIT has some men on secondment from the Special Boat Squadron.

Continuity

 * The Third Doctor, Jo Grant, Mike Yates and UNIT previously encountered another animated stone statue at Devil's End, called Bok. (TV: The Daemons) The Weeping Angels were another race of stone statues, who became animated when they were not being observed. (TV: Blink, et al.)