Vaduz aired on BBC Radio 4 on 23rd January 2013 and starred:
- Benedict Cumberbatch as Martin
- Roger Allam as Douglas
- John Finnemore as Arthur
- Stephanie Cole as Carolyn
- Matilda Ziegler as Princess Theresa
- Anthony Head as Herc Shipwright
- Kieran Hodgson as King Maximillian
- Dan Tetsell as Karl/Otto
There is no pre-credits sequence for this episode. It opens with Carolyn and Herc going on holiday and leaving MJN in the hands of Martin, Douglas and Arthur. The phone rings and it's Princess Theresa of Liechtenstein on the phone, wanting them to come to the country, pick them up and take them back to England. At first, Martin thinks it's a prank and so does Douglas, until Martin does a quick Google search and then apologises.
Meanwhile, on their holiday, Herc vies for Carolyn's affections, but is growing increasingly frustrated that she isn't reciprocating. Back in GERTI, Arthur is practicing his bowing, Martin has been reading up on protocol and is wearing his old Air Cadets medals. They order 3000 liters of fuel for GERTI, then go and pick Theresa and Maximillian up from Vaduz Castle. They find that the King is going back to school and is very much like a child, which keeps Arthur on his toes.
Driving back to GERTI, Theresa flirts with Martin and adds more medals to his growing collection. Arthur and Maximillian play "Yellow Car", where he cheats. Once they get back to GERTI, they find that they have too much fuel inside GERTI, as Martin ordered 3000 liters, which means they can take off, but can't land in Fitton. Martin explains to Theresa in the flight deck, but she already worked it out, given the fact she wanted to be a Pilot as well. Meanwhile, Arthur and Maximillian are playing top trumps, which Maximillian is cheating at again, giving himself all 10s for his own card.
Carolyn returns to the Portacabin to see GERTI flying round in circles. She rings the satcomm onboard to find out what's going on. Theresa answers the phone and yells at Carolyn that they won't be accepted at any old airport and especially without security measure in place. Carolyn apologises and gets to it. Martin plucks up the courage to ask Theresa out on a date, to which she accepts. Martin is in shock