Erasure is out now from the Big Finish website (only) at £2.99 a download.

The Celestial Intervention Agency, a shadowy, unspoken of part of the Time Lord hierarchy. Beloved and loathed in equal measure by various Presidents and High Councils the millennias over. But they serve a very important function: they keep the time lines safe and clear – they do the darker, dirtier jobs that most Time Lords would prefer not to know even need doing.

CIA Sub-Coordinator Narvin has always taken his oath to uphold the Worshipful Laws of Gallifrey very seriously. But when he is sent on a mission to investigate the planet Bellascon, even he hasn't reckoned with the force of nature that is the Fourth Doctor, who has – one might say – his own way of dealing with things, and his own views on people like Narvin. But somehow the two must overcome their instincts and work together to stop the web of time being erased forever…

Producer Ian Atkins tells us all about bringing the Celestial Intervention Agency to the Short Trips range: "This all happened because of Seán turning up at the Big Finish office to do a podcast and being a very lovely chap and hinting that Narvin would be great in a Short Trip. Seán has one of the great Big Finish voices, so it didn't take much persuading! This was slightly unfamiliar territory for me, as I wasn't overly familiar with the early days of our Gallifrey range (which is when I wanted this set) and so I went to the expert in these matters, Gary Russell. He agreed to write and direct it, and before I knew it I was heading to Cardiff for a hugely enjoyable recording and then a hugely enjoyable lunch.

"Gary may not remember how kind and encouraging he was to a young fanzine editor in 1984, but I've never forgotten and it was a delight to work with him in an official capacity, and bring such a clever story to life. And kudos too to the sound designer David Roocroft, who's done a glorious job in making Narvin's world so very real – and dangerous!"

You can get this new adventure for £2.99 on download (only) out now from Big Finish. Or you can save money with a subscription to the Short Trips range and get 12 stories for £30 a year.

Coming next in Doctor Who: Short Trips, Trap for Fools, read by Mark Strickson.

‘…St. Neot’s Refuge was founded in 3016 for the education of young men to the service of empire and state. In the quiet shade of Diaz’ world, each boy can develop that true sense of self-worth which will enable him to stand up for himself, and for a purpose greater than himself and, in doing so, to be of value to society; to be a man…’ School Prospectus

“Want to change the future, Turlough? Use a school.” The Doctor