One character, imprisoned but with vital information on how to defeat the baddie, is able to send a message in Morse code:
'GRAB HARRISON'S PEN.'
The character receiving the message comments that he's never been so glad to see a full stop in his life.
It took me a couple of seconds to get it.
This is a kiddies' programme!! Outrageous.
It was a superb episode, with a witty twist on the old 'mysterious must-have technology' story, Peter Bowles!, and some touching but not overdone tearjerkery before the end credits.
A fitting finale to the series, even though its being the finale was tragically unexpected.
Finally, it's reassuring to learn that K9 is backing up the Bodleian Library.