In the scene where the Doctor and Rose meet the Queen's guards, the Doctor slips into a Scottish accent, which is a reference to actor David Tennant's heritage. Michelle Duncan and Jamie Sives were unable to attend the readthrough for this story, and their parts were read by Tennant's parents, who happened to be visiting the "Doctor Who" set. Tennant told reporters at the series' press launch, "Because it's set in Scotland they were delighted to be asked to read in. My mum played Lady Isobel and my dad played Captain Reynolds and they were in seventh heaven. And they were genuinely cheesed off when they didn't get asked to play the parts for real! I was like, 'Chill-out, Mum and Dad, back in your box!'"