The Secret of Cassandra was the seventh Bernice Summerfield audio story produced by Big Finish Productions. It was also the first original audio story produced for the series. This was writer David Bailey's first contribution to a Doctor Who universe story; he continued on to contribute to a range of Doctor Who elements including further Bernice Summerfield stories and Doctor Who Magazine and Doctor Who novels.
For the entire guest cast, this is their only Bernice Summerfield audio story; they have all however appeared in other Big Finish audio story productions.
A vicious war between two nations is coming to a head, and the final movements are centred on the sailing ship Cassandra. Along with a very strange cargo, Cassandra carries Captain Colley, a man with his own sad burden, and the paranoid General Brennan, a woman convinced that her actions will end the war once and for all. Their grim mission goes entirely to plan, until the Cassandra gains an extra passenger - a shipwrecked archaeology professor by the name of Bernice Summerfield.
Sensing something is very wrong aboard the ship, Bernice's snooping brings her close to a terrible truth. Soon, Bernice doesn't know who to trust, and she can no longer be sure if anyone is who they claim to be...
Bernice is on vacation on the Earth colony, Chosan. Two of the planet's continents, Pevana and Calabraxia, are at war with each other. Benny has been stranded on a desert island for two days after her boat was shot down because she was drifting into enemy territory. The captain of Cassandra sees her and insists on picking her up despite his only passenger's protests.
Benny wakes up on the ship. It is a high tech vessel despite the exterior looking like a 17th century sailing ship. The ship is full automated, thus there is no crew. The ship also refers to the captain as "Dad".
The only other passenger, General Hannah Brennan, fears that Benny is a spy. Benny and Captain Damien Colley discuss the war. Colley is tired of the war. His daughter, the original Cassandra, designed the ship's AI, but was killed in the war. The shock of their daughter's death slowly killed his wife as well. Meanwhile, we learn that Brennan is holding a prisoner named Sheen in the cargo hold.
Benny contacts a nearby Pevenan ship and tells them about the prisoner. Brennan continues to suffer from extreme headaches and loses consciousness. Benny attempts to let Sheen free, but he doesn't seem to desire escape. She eventually takes him to the deck, although this confuses the ship's AI, as she was originally unaware of his presence on board. The man then powers up one of the ship's staser cannons, which he uses to blow up a ship full of his own people.
Brennan reluctantly admits that she worked undercover as a Pevenan for over a year. Sheen was the head of a project to develop a superweapon capable of destroying the entire Calabraxian continent, but Brennan kidnapped him and is taking him to Calabraxia for interrogation.
Sheen admits he is responsible for Brennan's headaches. Her memories had been blocked, and it causes pain when she tries to remember something about Sheen. Sheen's eyes are covered in cataracts, due to an operation that turned him into the walking, living bomb which will destroy Calabraxia in ten hours' time. Cassandra removed the memory block from Brennan's mind.
Colley reveals that the whole time he was trying to avenge his daughter's death by killing the Calabraxians. Sheen then comes out with an even more shocking revelation, he is in fact the original Cassandra. She transferred her mind into the manufactured body of Sheen in order to continue working on the weapon. Upset and unable to handle this knowledge, Colley then shoots Sheen.
In order to dismantle the bomb inside Sheen, Cassandra uploads her intelligence into Sheen's body. She is able to do this because Sheen's AI network and her own were designed by the same person.
- Bernice Summerfield - Lisa Bowerman
- Captain Damien Colley - Lennox Greaves
- General Hannah Brennan - Sally Faulkner
- Computer - Helen Goldwyn
- Sheen - Robert Curbishley
to be added
- Two covers exist for this audio. The original is semi-photographic and features Lisa Bowerman's face. The second is a pure illustration by Adrian Salmon. Following this story, for a number of series, all audio covers were designed by Salmon. In the 2010s, however, Big Finish returned to mainly photographic covers, rendering moot the effort to "standardise" Bernice Summerfield covers.
- This audio drama was recorded on 26 August 2000.