Professor Bernice Summerfield and the Poison Seas (audio story)

, or simply The Poison Seas, was the third audio story of the fourth season of the Big Finish Bernice Summerfield series. It featured the Sea Devils, the first performed story to use them since the 1984 Doctor Who television story Warriors of the Deep. It was set on the planet Chosan, the setting for Big Finish's first original story, The Secret of Cassandra.

Publisher's summary
Bernice has visited the planet Chosan before, so she seems the ideal candidate to intervene when a Sea Devil colony there comes under threat from a terrorist cell. Under cover of visiting an old friend, Bernice sets out to learn who is working in league with the terrorists to ensure the eradication of the colony.

But as she delves deeper under the oceans of Chosan, she discovers that something else — something much more ancient and powerful — ­wants rid of the Sea Devils. Soon, every living thing on the planet is in peril. And all because there's no place like home...

Plot
Sent by Braxiatel to assist the Earth Reptile Council with a terrorist cell on Chosan, Benny tells Joanne Carver that she intends to visit her friend Earth Reptile friend Clinician Nedda in the seabed complex and employs her to transport her there in a submarine. Benny finds Nedda, who has been researching a protein in the seawater which has been mutating her people, and they come across the body of Security Officer Torkilis as they go to speak with Principal Lurnix. Nedda attempts to raise the alarm, but her authorisation code does not work.

Carver, having followed Benny to the base and shot Torkilis, contacts Lurnix, who wants to destroy the base in order to give himself an excuse to return to Earth. She confirms that she has planted a bomb which will detonate in two hours, giving the two of them enough time to escape, but, whilst she is updating Peterson by comms system, sharks attack her submarine and it is flooded. She is uncertain of Peterson's fate and informs Lurnix that the plan will have to be changed.

Benny explains to Nedda and Lurnix that the Pevanan Secret Service have become aware that Calabraxian terrorists, led by Carver, intend on attacking the Earth Reptile base and believe that they have a contact there. Afterwards, she shares with Nedda that she is suspicious of Lurnix and is told by Nedda's assistant, Ressix, of the protein and how he believes that its effects can be halted at a particular stage. Benny and Nedda find Lurnix exhausted at the Earth Reptile shrine and talking about how the water can make the Earth Reptiles better. Whilst Benny goes to find Carver, Lurnix reveals that he is the protein and tries to kill her, but Ressix saves her and, after killing him and lowering the security grid, Lurnix sends out his people to find her.

Carver captures Benny and ties her up, leaving her with the bomb and going to find Lurnix to escape the base with him before the detonation, but he attacks her and orders the opening of the aqua locks. After Nedda frees her, Benny has Nedda get the Earth Reptiles to safety in the caves and finds Carver, telling her about the protein and how it could end life on land as well as in the sea. She and Carver escape the base before the detonation and plans on telling the Earth Reptile Council to rehome the Earth Reptiles on Chosan to an uninhabited planet to make their home.

When Benny contacts Braxiatel, he claims that everything is okay on the Braxiatel Collection but asks her to return as soon as possible, which worries her. She leaves Nedda with Carver, who is to be taken to face legal consequences for her actions.

Cast

 * Bernice Summerfield - Lisa Bowerman
 * Irving Braxiatel - Miles Richardson
 * Principal Lurnix - Ifan Huw Dafydd
 * Clinician Nedda - Nicky Goldie
 * Joanne Carver - Jenny Livsey
 * Ressix - Matt Dineen

Continuity

 * Bernice was last on Chosan approximately four years earlier in AUDIO: The Secret of Cassandra.
 * The Sea Devils were introduced in TV: The Sea Devils.
 * Bernice keeps the Time Rings which the Seventh Doctor gave to her and her ex-husband Jason Kane as a wedding present in her wardrobe. (PROSE: Happy Endings)
 * When telling her that the universe serves curve balls, she tells Nedda that she was a man once (PROSE: The Squire's Crystal) and the mother of a messiah. (PROSE: The Glass Prison)