The Secret History (audio story)

 celebrated the 200th release in Big Finish Productions' monthly range. It partnered the Fifth Doctor with First Doctor companions Vicki Pallister and Steven Taylor, and concluded the "Locum Doctors" trilogy.

Publisher's summary
The TARDIS brings the Doctor, Steven and Vicki to the Italian city of Ravenna in the year 540 – besieged by the army of the celebrated Byzantine general Belisarius. Caught up in the fighting, Steven ends up on a boat bound for Constantinople, the heart of the Roman Empire.

Rescuing Steven, however, is the least of the Doctor's problems – because he shouldn't be mixed up in this particular adventure at all. Someone has sabotaged his own personal timeline, putting him in the place of his First incarnation... but who, and why? The truth is about to be revealed – but at what cost to all of the Doctors, and to the whole future history of the planet Earth?

Part one
Vicki Pallister and Steven Taylor run into the TARDIS, while being shot at. Inside, however, they find the Fifth Doctor instead of the First. While the aliens bang on the doors, the Doctor dematerialises, then references past adventures, proving to his companions he really is the Doctor. He explains he was just in his own TARDIS, then appeared in this one. They land, and the Doctor already knows where they are: Ravenna, Italy, 540. He remembers that trip, but as soon as he leaves the TARDIS, the timeline will change to one in which he didn't experience these events in his first incarnation, and thus he'll forget everything that's about to happen.

They step outside and the Doctor gives some historical background about Ravenna and the split of the Roman Empire. The city is about to be sieged by the Romans.

Flavius Belisarius is preparing to invade Ravenna under the guise of negotiation, and tells his advisor Procopius that he must come as well.

The Doctor watches Belisarius enter the city and head to the palace. He and his companions follow the crowds there.

Quintis join Sophia in her room and they go onto the balcony. Quentis gives her a crossbow, and says to protect the Doctor, Vicki and Steven.

Belisarius enters the palace and claims the city. Procopius goes outside and informs the crowd about what has happened, and that if they cooperate, they will be left alone. The people take up a cry of "No surrender!" and the Doctor and his companions move back to the TARDIS. A man confronts the Doctor, and is about to attack him as a traitor to Ravenna when he is shot by Sophia's crossbow.

Steven gets separated, and accidentally offends another man, who knocks him out.

Vicki and the Doctor get to the TARDIS, and find Procopius hiding behind it. The Doctor goes back into the crowd to look for Steven, and Procopius recounts the story of the capture of Carthage to Vicki.

Steven is woken up by a physician, who is confused by Steven's requests for the Doctor.

The Doctor returns to Vicki and Procopius, unsuccessful. Procopius takes him for an audience with Belisarius while Vicki continues the search in the crowd. Belisarius tells the Doctor that Steven could have been mistaken for a Goth, and all Goths were put on a boat to Constantinople.

Vicki finds a woman who has seen Steven been put on a boat for Constantinople with the other injured. As a cover, Vicki says she and Steven have eloped, and the woman Sophia is going to Constantinople soon. She's from Greece, and she left there with a stranger who understood her.

Steven wakes up again, and the doctor who rescued him identifies himself as Quintis. They're on a ship to Constantinople, and when they get there Quintis will explain to the captain that Steven isn't a Goth, so he will be free, but still stranded.

A message arrives for Belisarius from Emperor Justinian. The emperor wants him to end the siege and return because Constantinople is under threat from the Persians. Belisarius refuses, but the Doctor convinces him otherwise. Procopius agrees to let the Doctor and Vicki travel with them.

At the port, Belisarius refuses to bring the TARDIS on board. The Doctor explains to Vicki he only changed Belisarius's mind because he knew it was supposed to happen that way. Vicki spots Sophia in the port.

Steven is amazed by Constantinople. Quintis tells him he can find employment at the chariot races with his friend Yazid.

The Doctor and Vicki arrive in the city. As they leave the ship, he's arrested by imperial guards.

Quintis meets with Justinian. He has told the emperor the Doctor is a Persian spy, and Justinian will have him put to death.

Part two
to be added

Part three
to be added

Part four
to be added

Cast

 * The Doctor - Peter Davison
 * Vicki - Maureen O'Brien
 * Steven - Peter Purves
 * Sophia - Lysette Anthony
 * Theodora - Sarah Woodward
 * Procopius, Yazid - Tony Millan
 * Belisarius - Giles Watling
 * Justinian - Tim Wallers

Continuity

 * The Doctor refers to when he told Vicki to give Barbara another chance after she shot Sandy (TV: The Chase) and their trip to Rome. (TV: The Romans)
 * The Doctor tells Vicki he cannot change history, because if he did the Roman Empire may survive to her day. His fourth incarnation encountered an alternative Roman Empire in the 1970s. (COMIC: The Iron Legion)
 * The Doctor is surprised he is the only one with a key to the TARDIS, and says that Vicki and Steven should have keys of their own. He would later grant keys to companions such as Liv Chenka and Rose Tyler, and had previously given one to Susan Foreman. (AUDIO: A Life in the Day, TV: Aliens of London, The Daleks)