And we’re back! The second of the first two-parter this season. When last we left, the Sontarans, using corrupt boy genius Luke Rattigan, had secretly used the ATMOS car system to release poison gas worldwide. Oh, and they’d captured Martha and put an obedient clone in her place to monitor UNIT. Donna and the Doctor were desparately trying to get her Gramps, Wilf, out of his locked car, as the London streets filled with clouds of gas and choking victims.

Well, Donna’s mom Sylvia solves the most immediate concern pretty quickly. She steps out of the house and smashes out the car window with an axe. See, Doctor, sometimes you’re too clever for your own good. Just ‘cuz your sonic screwdriver couldn’t open the car was no need to panic. The Doctor sends mom and gramps back into their house and tells Donna to wait in the TARDIS. He gives her a key and gets emotional only for Donna to take him down a peg by reminding him they have a problem to solve.

Unfortunately, the Sontarans quickly teleport the TARDIS (with Donna inside) into their orbiting battlecruiser, to keep The Doctor Earthbound. He doesn’t like that very much at all. Clone Martha arrives and takes him to UNIT headquarters so that he can figure out what to do about the gas. There, UNIT’s men have figured out that the gas becomes lethal at 80% density. In urban areas, it’s up to about 60% already.

UNIT makes the call to launch missiles at the Sontarans, but the Doctor is adamant that they’re outclassed fighting Sontarans and that that would be suicide. Unknown to the Doctor and UNIT, Clone Martha has control of their network with her high-tech Sontaran PDA and keeps stopping the missile launch. The Doctor speaks with General Staal via a videolink and sees that the TARDIS is aboard. He attempts to trick Staal into revealing his plan but is unsuccessful. However, he does speak about calling him with a special phone which the spying Donna realizes is meant for her. She sees the whole discussion on a TARDIS monitor and just before the conversation starts, we the audience see Rose for a split second silently screaming for the Doctor! Donna has the Doctor’s “super” cell phone but doesn’t know what his number is.

The Doctor, meanwhile, is reasoning out that the Sontarans are stopping the nuclear missiles and also have an unknown element in the poison gas. The Sontarans send down squads of soldiers to invade the warehouse and begin ripping through UNIT. UNIT’s guns won’t even work properly because the Sontarans have released in the gas a method of stopping combustion. Their lasers mow down lots of soldiers including the Doctor’s new friend last week, Ross.

Luke Rattigan returns to his academy to gather his students to go with the Sontarans to a new world, where he has set up a great breeding program. His crew isn’t too into that idea and they all abandon him. Luke teleports up to the Sontarans and Staal lets him know they were smarter than he thought. They were only going to use them for target practice. Luke teleports back down to Earth just in time as he realizes the betrayal. The Sontarans shut down the teleport pods.

The Doctor calls Donna and talks her through sneaking through the Sontaran ship to reactivate the teleport pods. This is the first time she’s had to be brave and do something like this on her own and it’s pretty tense and well-played. Back on Earth, UNIT isn’t just sitting around. They call on the Valiant, their massive helicopter/aircraft carrier and use it to push the gas away from urban areas in London. They also arm with non-copper bullets and go after the Sontarans. I was very happy to see that they acquitted themselves well, quickly putting the Sontarans on the defensive. Best soldiers in the galaxy my ass!

The Doctor uses the distraction of the counter-attack to head into the warehouse basement with Clone Martha and finds real Martha. He knew she was a clone from moment one and knew that they had to keep the real Martha alive so that the clone had access to her memories. He frees Martha, severing the connection and the clone begins to die. Martha convinces her clone in her final moments to turn on the Sontarans and the clone reveals the hidden element in the gas is what the Sontarans eat for food.

That’s the last piece of the puzzle that the Doctor needs and he figures it out. The Sontarans don’t want to ruin Earth at all, they just want to kill off all the humans so that they can use it as one of their cloning worlds and breed billions of new soldiers. Donna reactivates the teleport pods and the Doctor saves Donna and steals back his TARDIS, then zips over to Rattigan’s academy where he’s crying over the betrayal.

The Doctor grabs a bunch of Rattigan’s ATMOS terraforming system equipment and builds an atomospheric weapon that ignites the gas and burns it up in the upper atmosphere. The Doctor takes the weapon and teleports aboard the Sontaran starship. Donna begs him not to do it in person, but the Doctor says he has to give the Sontarans the choice to surrender before he ignites the ship atmosphere. Staal chooses death of course and the Doctor is forced to activate the machine. But at the last moment, Rattigan teleports the Doctor back and takes his spot, pushing the trigger and blowing them all up.

The Doctor, Martha, and Donna get in the TARDIS to take Martha home but as they’re finished saying their goodbyes to Martha, the doors lock shut and the TARDIS activates on its own accord!

I liked this one about as much as the first part. There was more action and that’s fun, but there was also not much use for Martha being around and she was wasted a bit, just like her appearance on Torchwood. I liked the character growth Donna’s naturally going through. The only problem I had was the Doctor’s ultimatum to the Sontarans. Did he really think they’d ever choose to surrender over death? Or was he simply pretending so that Rattigan would sacrifice himself? I’d like to think the Doctor’s kinder than that, but he can be manipulative too.

Anyway, a solid outing with great effects. I give it another 4 out of 5 sonic screwdrivers: