Happy Birthday, Christopher Eccleston!
'Aha!' said Serena.'I think I can help.'
She opened a locker in the TARDIS console and rummaged inside, emerging with a piece of square white card, which she handed to the Doctor.
He looked at it. ‘What’s this?’
'Whatever you want it to be. Look hard at it and concentrate.' The Doctor stared hard at the blank white square and concentrated. The card seemed to blur before his eyes – and suddenly he was holding a gold-edged, heavily embossed invitation card to the Duchess of Richmond’s ball.
'Latest Agency technology,' said Serena. 'Psychic paper – gets you in anywhere!'
'Splendid!' The Doctor tucked the square into his frock coat and they set off.
— Terrance Dicks, World Game (2005)
Originally introduced in the new series, psychic paper was used in World Game, a novel featuring the Second Doctor.
Happy Birthday, Billie Piper!
"I’m talking to a twig."