The Doctor and Donna are faced with arrest.

Then Shelda's trill voice pipes up. "By the Proclomation of Aavid-Norr, we place the Doctor under arrest"

The Doctor, Donna and Aattah turned round and saw Shelda aiming a pistol at them.
“You really know how to make friends, don’t you Doctor” sighed Donna

“You have no authority here Commander Shelda” Aattah shrilled, with obvious irritation.
“Stand aside Aattah, this doesn’t concern you” Shelda ordered

The Doctor turned to Donna and whispered “When I shout ‘Now’, Run to the TARDIS”
“What are you gonna do?” asked Donna
“I just said, I’m gonna shout ‘Now’!”
“I was kind of referring to the bit before that”
“I’m gonna… wing it. Aaaaah” and the Doctor quickly turned to face Shelda. “I see you have a Phoron reverse laser pistol. I’ve always liked them. And you know why I like them? I’ll tell you why I like them.” The doctor quickly whipped something out of his pocket. “They don’t like sonics”
And with that he flipped a switch on his sonic screwdriver and sparks flew out of the gun.
“Run!”
“I thought you were gonna shout Now!
“Not now, Donna”
Donna took her opportunity to run. She ran out of the door that Shelda had burst in from. She ran the way she came. She ran and hid and ran, until she finally got out of the city. And there was the familiar sight of the TARDIS.
Quickly, she opened the door and entered, but it was too late before she realised her mistake. Because no sooner had she entered, than the form changed into sand and melted away, taking her with it.