Heroes of Sontar (audio story)

 was the one hundred and forty-sixth story in Big Finish's monthly range. It was written by Alan Barnes and featured Peter Davison as the Fifth Doctor, Sarah Sutton as Nyssa, Janet Fielding as Tegan Jovanka and Mark Strickson as Turlough.

Released in April 2011, it was the first story in that year's trilogy of stories featuring the Fifth Doctor along with Tegan, Turlough and an older Nyssa who rejoined them in Cobwebs. This was the first Big Finish audio story to feature the Sontarans.

Publisher's summary
Planet Samur was once a peaceful haven. Pilgrims journeyed across the seven galaxies to meditate in the courtyards of the vast Citadel that spanned its equator. It was Samur's misfortune, however, to find itself situated on the furthermost frontier in the eternal war between the amoeboid Rutan Host and the belligerent, troll-like Sontarans...

Twenty years after detonating a bacteriological weapon over Samur, rendering it uninhabitable, the Sontarans are back: a select platoon of seven has landed here on a secret mission, carrying sealed orders given to them by Fleet Marshal Stabb.

The TARDIS has landed here, too, bringing the Doctor, Tegan, Turlough and Nyssa into the second great Battle of Samur. Fighting not only the Sontarans, but mystical mercenaries... and a deadly, decades-old curse.

Part one
Wanting to give Tegan some rest after the Mara, the Doctor pilots the TARDIS to the Citadel of Samur and finds it in a state of disrepair despite it only being thirty years after his previous visit. He tests the brittleness of the ground over which a purple moss has passed and accidentally creates a crevice which leaves the TARDIS inaccessible, indicating that the moss, which is everywhere, is weakening the Citadel at a molecular level.

Nyssa is interested in the moss and, in one of the many courtyards, she and Turlough locate a banner commemorating Samur's subjugation by the Sontaran Empire. She becomes infected by the moss and the two of them head back to the TARDIS for a biotronic agitator, but the ship is covered in moss. A Sontaran spaceship crashes after being shot by the Rutans, its crew escaping in gravity spheres, and the Doctor and Tegan are arrested by Field-Major Thurr after Tegan unwittingly gives away the Doctor's identity.

Part two
The Doctor surrenders to Thurr to keep himself and Tegan from being executed and manipulates him into setting out to gather all of the Sontarans' communicator crystals to get in contact with Sontar and clarify what is to be done with them. Nyssa is captured by Corporal Clun and Turlough falls into a ten-storey crevice with Trooper Vend, whose communicator he smashes to keep him from calling for reinforcements. When the Sontarans hear Trooper Nold being attacked over his communicator, they presume that Turlough has killed him.

Clun brings Nyssa and explains that the moss is Agent Z/002, a weapon which the Sontarans used to turn the Samurians and the six surviving Witch Guard mercenaries into moss twenty years ago, but Thurr believes that this and the possibility of the victims killing Nold for revenge is absurd. Tegan is taken hostage by Sergeant Mezz and tasked by the Doctor with stealing booster shots from the Sontarans' replenishment tank at the crashed ship to cure Nyssa, finding the corpse of Pilot Beck on the way. Beneath the ground, Turlough and Vend see a living darkness and run.

Part three
The Doctor and Nyssa learn from Clun of the seventh Witch Guard's curse, stating that seven Sontarans would have to die to avenge the deaths of the seven Witch Guards, and the Doctor tries to use four Sontaran communicators to contact the Rutans. Turlough and Vend barricade themselves in the crashed ship with Tegan and Mezz against the darkness, which transforms into a swordsman who kills Mezz and disappears after the Doctor's signal bounces against something in the stratosphere. The resulting sound also harms the Sontarans and Nyssa uses it to gain the upper hand.

Tegan, Turlough and Vend fire the ship's plasma cannons and launch the ship back to the Citadel, where Thurr deliberately spills the nutrients collected by Tegan in an empty container which supposedly held sealed orders and condemns her and Turlough to be executed. He is stopped by two Witch Guards, who reveal that Thurr and his men were sent by Fleet-Marshal Stabb to die to put an end to the curse. The Doctor, having left in a gravity sphere to find what it is in the stratosphere, attempts to contact the Rutans, but they fire at his ship despite him declaring himself a non-combatant.

Part four
to be added

Cast

 * The Doctor - Peter Davison
 * Nyssa - Sarah Sutton
 * Tegan - Janet Fielding
 * Turlough - Mark Strickson
 * Fleet Marshal Stabb / Trooper Jorr / Witch Guard - John Banks
 * Field-Major Thurr / Adjutant / Orbital Command - Duncan Wisbey
 * Sergeant Mezz / Trooper Nold - Alex Lowe
 * Corporal Clun - Andrew Fettes
 * Trooper Vend - Derek Carlyle

Individuals

 * Tegan's aunt Vanessa was seemingly fond of saying, "Bog off."

Planets

 * The Doctor visited Samur approximately thirty years earlier.

Timeline

 * It is the Sontaran martial year 5709.

Continuity

 * This marks the first time that the Fifth Doctor faces the Sontarans in his personal timeline. He would later do so again in AUDIO: The Five Companions, PROSE: The Eight Doctors and PROSE: Lords of the Storm.
 * Tegan claims that the Mara is no longer in her system. (AUDIO: The Cradle of the Snake)
 * The Sontarans are still angry about "that Gallifrey incident." (TV: The Invasion of Time)
 * Nyssa tells Tegan that she is married to a man named Lasarti and that they have three children named Neeka, Tegan and Adric, who is the youngest and a teenager. Furthermore, she implores Tegan not to tell the Doctor in order to maintain the Web of Time as he will not find out that she was married until shortly before his regeneration into the Sixth Doctor. (AUDIO: Winter)
 * The Doctor refers to his encounter with Jingo Linx in the 13th century during his third incarnation. (TV: The Time Warrior)
 * Nyssa mentions encountering the Rutans in Stockbridge in 1199. (AUDIO: Castle of Fear)
 * Nyssa uses the name of her late father Tremas as her access password. (TV: The Keeper of Traken)
 * Turlough refers to the underground complexes on Heiradi. (TV: Frontios)
 * Turlough would later encounter the Sontarans for the second time in the Unukalhai system in 2371. (PROSE: Lords of the Storm)
 * Nyssa previously encountered the Sontarans in an alternative Death Zone on Gallifrey. This event has yet to take place in the Doctor's personal timeline. Notably, Nyssa does not appear to remember this incident. This is consistent with the Doctor's statement that her memory of her experience in the alternative Death Zone would most likely be hazy after she was returned to her rightful place in history, namely Terminus in the 35th century. (AUDIO: The Five Companions)
 * Previous Sontarans the Doctor has met are mentioned, one Sontaran prays by the name of Linx (TV: The Time Warrior) and the Fleet Martial says the Doctor is to be tortured in accordance with the works of Field Major Styre. The Doctor was unaware Styre had published them. (TV: The Sontaran Experiment)
 * As a Junior Ensign Commander, Turlough outranks some of the Sontarans on Samur. (TV: Planet of Fire)