Did you spot the Torchwood reference in this week’s Doctor Who?

In Face the Raven, it was revealed that graffiti artist Rigsy (Jovian Wade) had been enticed to a hidden street and drugged, losing his memory of the entire incident. The drug used to remove the memories? Retcon – also known as Compound B67 or the amnesia pill, and a favourite of Torchwood Three for mind-wiping anyone unlucky enough to stumble on their operations.

Interestingly, retconning also refers to the practice of TV shows, comic books and films (or anything with a narrative really) reinterpreting previous events to fit in with the latest version of the story – for example Peter Capaldi's Doctor choosing to have the same face as Roman patriarch Caecilius and bureaucrat John Frobisher – so it was already a bit of an in-joke when it was used in Torchwood. In-jokes within in-jokes!

Anyway, the fictional drug was used in several episodes of the spin-off to remove the memories of various people (including lead character Gwen Cooper in the series premiere), and was last seen in Torchwood’s final ten-part series Miracle Day back in 2010.

Whether it was to forget an evil alien, confess secret affairs or just keep the organisation out of the public eye, Retcon was a pretty major part of Torchwood, but until now had never appeared in an episode of Doctor Who – so how did it end up in the hands of Maisie Williams' Ashildr?

Perhaps, as predicted by Peter Capaldi’s Doctor in The Woman Who Lived earlier this series, fellow immortal Captain Jack Harkness finally found his way round to Ashildr and she picked up a few of his tricks. Or maybe since the dissolution of Torchwood Retcon is simply more readily available to the public – who knows?

Whatever the truth, we’re just glad to see Doctor Who paying a fun little tribute to its spin-off. We were getting worried it might have forgotten...

Doctor Who continues next Saturday at 8:05pm