Dennis Spooner makes a smart decision to begin this story about a month after the previous episode’s cliffhanger. It means when we re-join them, Vicki has had weeks to get to know the Doctor, Ian and Barbara.

As both writer and incoming script editor for this episode, Spooner uses the opportunity to ring the changes from the old regime. This is most clear in the treatment of Ian and Barbara – originally the viewpoint characters introducing us to the world of the ‘unearthly child’ and her mysterious old grandfather, they’re now relegated to the position of the old fogeys. Vicki accuses Barbara of being ‘as bad as Ian’ and opines that their Roman sojourn is ‘boring’. She’s desperate for the adventures she was promised. This very firmly aligns her with the Doctor, who’s shaken off the indolence of life in a country villa and is determined to head for the bright lights of Rome itself. And while he seems keen to have a few days away from the cosy domesticity of Ian and Barbara, it takes practically no effort for Vicki to convince him to take her along for her ‘first exploration’.

It’s hard to shake the feeling that this is part of a broader realignment of the series, more attuned to Spooner’s taste in comedy and ‘telefantasy’. The Slave Traders is practically a sitcom for half its run time, with a couple of very funny sequences of the Doctor pottering around the villa winding Ian up, and waxing lyrical about Barbara’s cooking – until he learns what’s in it. Even dramatic moments have a strong element of farce – as when Barbara bashes Ian over the head with an urn, or when the slave traders have to barter with an avaricious shopkeeper to get information. Like Spooner’s work on The Avengers and later ITC shows, what in other hands might have been quite a serious and slow script is leavened with a lot of humour and physical comedy, and terrible puns (‘She keeps her eye on all the lyres’), so that one of the less eventful episodes to date is also one of the most amusing.

That said, towards the end of the episode, even while the Doctor and Vicki are amusing each other with his lyre playing, grim historical reality creeps in as Barbara reflects on the horrors of Roman slavery and the improbability that there will be a way out for her and Ian now they’ve been kidnapped to be sold. Beneath all Spooner’s comedy is a very dark, rather hard edge that prevents this from being just frothy silliness, and introduces a necessary sense of peril.

Next episode: All Roads Lead to Rome