"Wasn't I clear last time? Unless you're a crossover, you aren't
permitted to enter!"

This time, it was Mark's turn to smirk at Polly. "I think you're
making a mistake - I _am_ a crossover now."

Polly gaped. "WHAT? You said it yourself - NOBODY would write a
Doctor Who/Battle of the Planets crossover!"

Mark grinned and pointed to an entry at the bottom of Polly's
clipboard. "Not so. I just appeared in 'Who Force' - with you as a
matter of fact!"

Polly frowned. "You think that appearing in a This Time Round story
counts as a crossover?!? I've got some bad news for you -"

"I'm afraid that the bad news is for you - if you look in the
Archivist's Notes after the story, you'll see that it was listed as a
Crossover. Therefore I already have appeared in a DW crossover. Now
if you'll excuse me - I'm rather thirsty."

As Mark pushed past her, Polly shouted after him, "That's not
fair! That whole previous piece was written just so you could get
inside in _this_ piece!"

Mark just smiled and waved.