Here are a few spilers which are all true from Digital Spy:
Donna Nobis Perchum
After bidding goodbye to her family yet again, Donna is ushered into the TARDIS by the Doctor for safe-keeping until the storm blows over. Unfortunately, she's not got her feet up for long, as the Sontarans - aided by Martha's clone buddies - teleport the TARDIS to their ship above the Earth.
The clue's in the name.
As the fumes from Atmos engulf the planet, the nations of the world unite to launch a nuclear strike against the Sontaran ship. The Doctor knows that the nuclear missles will have no impact, but his pleas to stop the strike fall on deaf ears. Expect lots of shouting from Mr Tennant this episode, by the way - he's scary when he's impassioned! The Doctor also realises that the gas is being used by the Sontarans for a secondary purpose - but what exactly are they planning for the Earth?
Freema? Think again
When all is done, Martha Jones is ready to go home to her waiting fiancé. But in a surprise twist, she is not allowed to. Physically not allowed to. Three's a crowd, eh?p
Who Said What?
Here are some select quotes from the episode, with the obligatory blanks left in to keep you wondering. Commence speculation!
"She's not like you. She's not a *******."
"My God, they're like trolls."
"I've designed a ****** program."
"The ******* of ****** is ******* nonetheless."
"Isolate them as they perish."
"Are you my *****?"
"We've lost our target practice."