Doctor Who has a tradition of running prequels each season that tease upcoming moments. The prequel to the season finale airs this Saturday.

Earlier this year we were treated to Victorian Era prequels that gave us the backstory of Jenny, Vastra, and Strax. The first one related how Strax was resurrected and they came to work together. In the second one, just before Christmas, Jenny, Vastra, and Strax demonstrated how they passed themselves off to London society.

Just before the second half of the season began in March, there was also a Clara and Doctor centric prequel where the Doctor encountered a 10-year-old or so Clara, on a swing-set at a park.

So, we are now up to the fourth prequel since December. The BBC is promising that this one will be the longest and most detailed one yet.

Written by Doctor Who’s lead writer and executive producer, Steven Moffat, the intriguing prequel is called “She Said, He Said” and stars Matt Smith as the Doctor and Jenna-Louise Coleman as Clara. It’s one of the show’s longest prequels and explores how little Clara knows about the Doctor… and vice versa.

Not a lot is revealed in the above synopsis, and even less is gleaned from the official still from the prequel below.

There will be a couple of viewing options. Anyone who lives in the U.K. can see the episode using the BBC’s “red button service” right after “Nightmare in Silver” concludes at 7:45pm GMT (2:45pm EST). Additionally, the BBC is promising to put the video online at the official Doctor Who site (generally they have done this via their YouTube channel). This year, the site has not been region blocked, so anyone, at least this year, can view the content.

The one thing that spoiler-phobes are going to have to be aware of is that this prequel will presumably be able to be viewed prior to the U.S. airing of “Nightmare in Silver.” It may or may not include spoilers for “Nightmare in Silver.”