These reviews are based on the UK broadcast of the series, which is several episodes ahead of the US broadcast, so beware of spoilers.
PART 1 SUMMARY:
The Doctor is called back to Earth by his former companion, Martha Jones. Martha now works for UNIT (Unified Intelligence Taskforce), a military organization charged with protecting the planet from alien threats. Donna is surprised to learn the Doctor also worked for them some years ago.
UNIT has just taken custody of an ATMOS factory. ATMOS (Atmospheric Ommision System) is a device developed by child prodigy Luke Rattigan. It can be installed in any make of car and combines a system that reduces emmisions to zero with a satellite navigation system. UNIT has received information concerning fifty-two deaths that took place around the world simultaneously. Each victim had ATMOS in their car and died of poisoning by an unknown and untraceable substance.
Two UNIT soldiers, Privates Harris and Gray, are investigating the lower level of the factory when they find a room containing a mysterious tank, which opens to reveal a faceless humanoid floating in a green liquid. Private Harris deduces that someone is growing themselves a human body. Another humanoid in armor arrives, and due to it's short stature Harris assumes it to be a kid playing a prank until the new arrival uses a weapon to disable his legs, then Gray's. The alien says he will put them to use for a greater purpose.
Martha suggests to Donna that she tell her mother and grandfather about the Doctor, something Martha didn't do which led to a situation that nearly destroyed her family. Donna sets off for home while the Doctor travels to the Rattigan Academy - Luke Rattigan's private school for young geniuses - accompanied by UNIT soldier Ross Jenkins. Harris and Gray reappear, now hypnotically conditioned, and trick Martha down to the room on the lower level.
The Doctor and Ross arrive at the Rattigan Academy and take a look around. The Doctor is impressed by all the advanced work being done, and suggests that all of their innovations could be used to terraform a new planet. He also recognizes an object in Luke's main office as a teleport pod. He beams himself onto a ship filled with armored aliens, then quickly teleports back, followed by one of them. The Doctor disables the teleport pod and identifies the alien as a Sontaran. The Sontaran identifies himself as General Staal of the Tenth Sontaran Battle Fleet. The Sontarans are among the best soldiers in the galaxy, a cloned race entirely dedicated to war. Their only weakness is a probic vent on the back of their neck that allows them to feed on pure energy. The Doctor bounces a tennis ball off the teleport pod, striking Staal in the vent, giving the Time Lord and Ross time to escape.
Back at the factory, another Sontaran named Commander Skorr connects Martha up to a device that creates a clone, complete with her memories but programmed with Sontaran directives. They will use this clone to infiltrate UNIT. Staal learns that their enemy is the Doctor, and is pleased that the last of the Time Lords will die at the hands of the Sontaran Empire.
The Sontarans take control of the ATMOS in the UNIT jeep, intent on driving the Doctor and Ross into the river, but the Doctor confuses the computer with a logical conundrum, allowing them to escape.
Making their way to Donna's home, the Doctor calls Martha to inform UNIT that they're up against the Sontarans. What he doesn't realize is that he is talking to the Martha clone, who does not relay his warning to Col. Mace. The Doctor investigates the ATMOS in the Noble family car and discovers it's secret: a temporal pocket. The Sontarans detect this interference and prepare to advance their plans.
Donna's grandfather, Wilfred Mott, tries to move to car off the road, but is locked in by the ATMOS. Suddenly all the cars in the street begin to pour out exhuast, along with all cars around the globe with ATMOS installed. The Doctor stares on in horror as the gas grows thicker and Wilfred is slowly being choked to death...
PART 2 SUMMARY:
The Doctor is unable to turn off the ATMOS, but Donna's mother Sylvia returns with an axe, busting the windshield so that Wilfred can escape. Sylvia begs Donna to stay with them, but Wilfred tells her to go with the Doctor, and the pair head back to the factory in an old taxi, the only car Ross could find without ATMOS.
When they arrive, the Doctor gives Donna her own key to the TARDIS and tells her to take refuge in there. The clone Martha belatedly relays the Doctor's message "Code Red: Sontaran" to Col. Mace. The Doctor plans to board the Sontaran ship, but Martha-clone has the conditioned Harris and Gray attach teleport transmitters on the TARDIS, enabling the Sontarans to capture it.
UNIT has ascertained the location of the Sontaran ship, but the Doctor says a nuclear strike would be futile. Instead he makes contact, asking the Sontarans what they're really up to since they could just as easily attack by force, and suggesting that they're losing their longtime conflict with the Rutans. General Staal fires back with the declaration that they have captured the TARDIS. What they don't realize is that Donna is inside also tuned in to the Doctor's transmission, and he attempts to communicate with her in a covert manner the Sontarans interpret as mere babbling.
Back at the Rattigan Academy, Luke informs the students of his grand plan: he's been having them prepare for an exodus to a new planet where they can build their own society. The students dismiss him as mad, and even thought he threatens them at gunpoint, they walk out.
News stations across the globe report that people are fleeing the cities en mass, heading for open country or the ocean in an attempt to escape the ATMOS fumes.
Despite the Doctor's protests, UNIT prepares to launch a nuclear strike against the Sontarans, but Martha-clone has hacked into the defense grid and stops the launch. Inside the factory, a Sontaran battlegroup engages the UNIT soldiers. With all projectile weapons rendered ueless by a signal that expands copper bullets, the troops are massacred as they retreat. The nuclear grid is reestablished, but Martha-clone deactivates it once again.
Luke returns to the Sontaran vessel reporting his failure, but Staal reveals that they were only using Luke for distribution of the ATMOS. They had no intention of transporting him and the students to another planet. Luke escapes before they can shoot him, and the Sontarans lock off all teleport links to Earth.
The Doctor calls Donna and tells her he needs her to infiltrate the ship and reactivate the teleports. Armed with a mallet, she knocks out the Sontaran guarding the TARDIS. She makes her way through the ship, but has to hide from a Sontaran patrol.
Meanwhile Col. Mace rolls out some new ammunition that will circumvent the corderlain signal. After giving a peptalk to the troops, he orders the UNIT flying carrier Valiant to clear away the smog around the factory. The soldiers enter the factory and are able to successfully fight off the Sontarans while the Doctor tracks down the alien technology hidden on the lower level where he finds the real Martha plugged into the clone machine. He tells Martha-clone that he realized what she was right away, and that he wanted her to stop the nuclear launch just as much as the Sontarans, in effect using her as a tripple agent. He unplugs the real Martha from the machine, cutting off her connection to the clone.
Donna phones back saying she's located the teleport control. While the Doctor rewires the pod, Martha gets the dying clone to tell them what the gas is made out of. The Doctor realizes its clone-feed, like amniotic fluid for Sontarans. They're converting the Earth into a hatchery where they can produce billions of new soldiers. Donna switches off the teleport deadlock and the Doctor is able to transport her and the TARDIS back.
They teleport to the Rattigan Academy where the Doctor explains that the Sontarans needed to prevent a nuclear launch to avoid setting fire to the volatile clone-feed now in the atmosphere. He uses equipment around the workshop to whip up an atmospheric converter, which he uses to burn off all the gas and purify the air. Although their plan has been thwarted, the Sontarans decide to launch an attack and wipe out humanity.
The Doctor recalibrates the converter for Sontaran air and bids goodbye to Donna and Martha, intending to sacrifice himself to save Earth. He gives the Sontarans a chance to leave peacfully, but they call his bluff. Luke enters the teleport pod, switching places with the Doctor and setting off the converter, which destroys the Sontaran ship.
Earth slowly recovers from the ordeal. People are now refusing to drive their cars, choosing to walk or bike instead. Donna says goodbye to her grandfather, who promises not to tell her mother so as not to worry her. Back at the TARDIS, Martha is there to bid her farewells, but before she can leave the TARDIS goes crazy and takes off on it's own...
Reveiw on Page 2
