Is The Riddle of the Sphinx the best-ever Inside No 9? It is certainly the cleverest. Too clever for words one could even say. How much you relish it may, however, depend on how much of a cruciverbalist you are.

Steve Pemberton takes centre stage as a Cambridge academic who also compiles the Varsity newspaper crossword. It’s a cryptic one which takes some completing and the prof takes great delight in setting the toughest and most circuitous of clues.

One dark and stormy night however, he is disturbed in his college rooms by an intruder. Nina, played by Alexandra Roach, wants a sneak preview of a forthcoming puzzle to impress her boyfriend. And so Prof Squires embarks on a lesson in how to work out each answer.

Of course, nothing is as it seems in Inside No 9 and as Squires goes through the clues the viewers may be working out clues to try to second guess what will happen next. Don’t bother. Just enjoy the drama as the plot twists and turns in this beautiful constructed playlet, directed by Guillem Morales and also starring Reece Shearsmith as one of Squires' oldest colleagues.

Instead of playing spot the clue you can always play spot the reference. I thought I sensed whiffs of Chekhov, Titus Andronicus, old horror film Theatre Of Blood and Anthony Schaffer’s Sleuth. But that might just be me. I might be totally barking up the wrong tree. The one thing you can be sure about with Inside No 9 is that they will always come up with something unexpected. Did I even spot a subliminal political message among the answers?* Not a word wasted.

News: Inside No 9 Teams Up With Guardian for Cryptic Crossword Coup

Inside No 9 – The Riddle of the Sphinx is on catch-up here.

Inside No 9 – Empty Orchestra Review.

*WARNING: SPOILER BELOW

*According to Steve Pemberton in The Guardian, "RIP NHS" was not political, they just happened to be Prof Squires' initials.