'The Poison Sky' (Story Code 4.5) by Helen Raynor

“This isn’t war – this is sport!” – Commander Skorr

As the skies fill with poisonous gas, Sylvia uses an axe to smash her car’s windscreen, saving Wilf from choking to death. At the ATMOS factory, the U.N.I.T. troops begin evacuating the gas-filled premises, while the evil Martha clone uses the military computers to download NATO’s security protocols and send them via her PDA to the Sontarans. The Earth’s governments declare a worldwide emergency, warning people to stay away from all cars fitted with the ATMOS device. Seeing the Doctor and Donna arrive in a black cab commandeered by Ross, the evil Martha finally passes on the Doctor’s message to Colonel Mace, warning him of the Sontaran invasion. Finally giving Donna her own key to the TARDIS, the Doctor sends his friend to his time-space ship while he goes to find the Colonel; however, the evil Martha despatches the hypnotised Private Harris and Private Gray to attach teleport pods to the TARDIS, transporting it and Donna to the Sontaran baseship. While General Staal is delighted at obtaining such a trophy of war, an excited Luke teleports back to the Rattigan Academy to begin the next phase of his own plan. Discovering that the TARDIS has been teleported away by the Sontarans, the Doctor and the evil Martha return to U.N.I.T. mobile command, where Captain Price advises that the gas becomes lethal when it reaches eighty percent density in the atmosphere. Tracing the signal for the ATMOS devices, Price locates the Sontaran baseship in Earth’s orbit; after warning Colonel Mace not to engage the Sontarans in warfare, the Doctor makes contact with General Staal, surmising that the Sontarans’ unusual tactics are due to losing in the fifty-thousand year war with their enemies, the Rutans. When Staal shows off the captured TARDIS the Doctor knows that Donna is listening via the ship’s scanner, and he inserts a coded message for her to use his mobile phone in his conversation with the General. At his academy, Rattigan reveals his master plan, “Planetfall”, to his acolytes; using the technology provided by the Sontarans, Rattigan will transport his comrades to the planet Castor Thirty-Six, dubbed “Earth.2”, where they will create a new human race; however, the team at the academy refuse to take Rattigan seriously, even when he pulls out a gun on them, and instead choose to leave to rejoin their families as the skies fill with poisonous gas. The worldwide crisis continues, and as the planet’s major cities become choked with toxic fumes, their populations abandon their cars and evacuate on foot. Donna phones her mother and learns that Wilf is sealing them inside their house. Back at U.N.I.T. mobile command, the Doctor and evil Martha analyse the gas and learn that it contains an unidentified element. With the gas now at sixty-percent density, Colonel Mace ignores the Doctor’s warning and orders a worldwide nuclear strike on the Sontaran baseship; however, as Price begins the countdown, evil Martha uses her PDA to override the launch. Commander Skorr takes an attack squad and teleports down to the ATMOS factory to engage in battle with the U.N.I.T. troops; the battle is one-sided, with the aliens’ Cordaline signal rendering the troops’ guns useless, and a massacre quickly ensues. When Ross manages to get a warning through to command before he is killed, the Doctor orders Colonel Mace to order a retreat; as the U.N.I.T. soldiers withdraw, Skorr guns down the hypnotised Privates Harris and Gray, gleefully watching as his men take command of the factory. Rattigan returns to the Sontaran ship, only to learn from Staal that he has been used – the Sontarans have no intention of taking him and his people to a new world. Staal orders Rattigan’s execution, but the tearful teenager manages to escape via the teleport, and so the General shuts down the link to Earth. Having deduced that the Sontarans have lured U.N.I.T. to the factory for their own ends, the Doctor borrows a soldier’s mobile phone and contacts Donna inside the TARDIS; with instructions on how to overpower the Sontaran guard outside the ship, Donna knocks out the alien with the TARDIS’ hammer and then makes her way through the ship. Back on Earth, Colonel Mace, the Doctor and evil Martha don gas masks and join the troops outside, who have now been equipped with ammunition immune to the Sontarans’ signal. Looking up, the Doctor is overjoyed to see the Valiant, U.N.I.T.'s helicarrier, descend from the gas-filled sky above, its powerful VTOL engines quickly dispelling the toxic fumes, clearing the surrounding area. As the Valiant opens fire on the factory, the U.N.I.T. soldiers storm the building and gun down the alien invaders, while Mace kills Skorr, allowing the commander the joy of a glorious death. Accompanying the Doctor to the Sontarans’ laboratory, the evil Martha pulls a gun on the Time Lord; however, the Doctor is unsurprised – he knew she was a clone from the start. Releasing the real Martha from the apparatus holding her, the Doctor severs the link between the two women, causing the clone Martha to collapse. As Martha tends to her duplicate, she manages to get the dying clone to reveal the truth about the ATMOS gas: it contains ‘clone feed’ – the Sontarans are changing the Earth into a clone world so that they can make billions of new soldiers. Aboard the Sontaran baseship, Donna reactivates the teleport controls, allowing the Doctor to transport her to safety seconds before two alien troopers open fire. While Martha uses her late clone’s PDA to prevent the nuclear strike, the Doctor returns the TARDIS to Earth and then transports himself, Donna and Martha to the Rattigan Academy. Disarming Luke, the Doctor uses the teenage genius’ equipment to begin construction of an atmospheric converter. Returning to his ship, Staal orders the ATMOS devices to be set to maximum, and the launch of the clone pods that will seed the planet’s atmosphere. Having calibrated the converter, the Doctor launches a missile into the Earth’s atmosphere; the device detonates in the sky, causing a colossal firestorm that burns off all the toxic gas across the planet before dispersing harmlessly. As the skies are restored, an enraged Staal instructs his troops to revert to Sontaran Stratagem One1 – to ravage the Earth. Recalibrating the converter to Sontaran air, the Doctor bids Donna and Martha goodbye and then steps into the teleport; arriving on the aliens’ vessel, the Doctor offers Staal the chance to withdraw, but the General declines – he does not fear death, and instead targets the Earth with every missile at his disposal. As the Doctor prepares to activate the converter, Rattigan uses the teleport to swap places with the Time Lord, sending the Doctor back to Earth while he activates the device – blowing himself, Staal, the Sontarans and their ship into a million pieces…

Some time later, as the Earth recovers from the invasion and everyone gets rid of their ATMOS devices, Donna bids goodbye to Wilf and rejoins the Doctor in the TARDIS; Martha is also inside the ship, saying farewell to her old friend before she leaves for home. But at that moment the TARDIS doors slam shut and the console activates of it’s own accord – out of control, the ship dematerialises…

David Tennant (The Doctor), Catherine Tate (Donna Noble), Freema Agyeman (Doctor Martha Jones), Bernard Cribbins (Wilfred Mott), Jacqueline King (Sylvia Noble), Ryan Sampson (Luke Rattigan), Rupert Holiday Evans (Colonel Mace), Christopher Ryan (General Staal), Dan Starkey (Commander Skorr), Clive Standen (Private Harris), Wesley Theobald (Private Steve Gray), Christian Cooke (Ross Jenkins), Bridget Hodson (Captain Price), Kirsty Wark (Herself), ATMOS Voice (Elizabeth Ryder)

Directed by Douglas Mackinnon
Produced by Susie Liggat
Executive Producers Russell T. Davies, Phil Collinson and Julie Gardner
A BBC Wales production

TX:
3rd May 2008 @ 6.20 pm

Notes:
*Featuring the Tenth Doctor, Donna and Martha

*Part two of a two part story

*As well as David Tennant and Catherine Tate, Freema Agyeman is also credited during the main titles

Bad Wolf sighting: as the TARDIS relays the Doctor's communication with General Staal to Donna via the scanner screen, we see a fleeting glimpse of Rose Tyler...