The final story in this set is far more in the mould that The Avengers would adopt increasingly over the next couple of years, with espionage events caught up in a more outlandish world, albeit one that’s more grounded than would prove to be the case later. Equally it shows the problems with trying to involve Keel in the adventures – once again he has to take time off from his surgery to help Steed. It’s tempting to think that having Steed partnered with one of his colleagues was crossing the producers’ minds by this stage, but you have to remember that the series started off as a vehicle for Ian Hendry’s Keel, not Patrick Macnee’s Steed!
Full marks to all involved for the tension in the third act as it seems as if Steed is in for a very close shave in the eponymous tunnel, although there’s an interesting use of gadgetry that doesn’t feel very 1962 (bear in mind Bond’s Q-provided briefcase wouldn’t appear in the 007 movies till From Russia With Love over a year later). There’s plenty of humour and opportunities for Anthony Howell to display Keel’s dry wit (his reaction to Steed’s undercover position is priceless), and the relationship between the two male leads is as strong as ever.
Once again, director Ken Bentley and producer David Richardson pull together a strong supporting cast, and there’s some neat use of descriptive dialogue from John Dorney and sound design from Richard Fox and Lauren Yason, particularly for what could easily have been a near-totally visual teaser.
Verdict: Another highly enjoyable step back in time. 8/10