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If you’ve never watched this curious series, don’t be afraid to start now – each episode is a fresh helping of twists, turns and intriguing incidents.

Tonight’s half hour is set in the quadrangles of Cambridge, where a professional crossword compiler gives an intruder a lesson in the art of complicated puzzles.

No Offence’s Alexandra Roach stars as Nina, the young lady trying to steal the answers to the crossword, while Steve Pemberton plays a knowing professor, aware from the start that the situation isn’t quite as it seems.

We don’t want to spoil the rest for you… but if you can guess how this gem ends you’re smarter than we are!