As this episode opens a woman and her granddaughter, Jitske, visit Professor T to ask him to help solve a murder. The woman's daughter was killed a few days previously and she believes Jitske knows who did it; unfortunately she has Down's syndrome and was raised never to speak badly of people. On the plus side she was also raised not to lie and agrees to answer one question so if the professor can find a prime suspect she will confirm his suspicion. The police have already arrested one suspect but he is soon cleared. Annelies wants to pressure Jitske into giving the information she knows but the professor is certain that wouldn't be of any use. The investigation soon exposes some cracks in the family but it will still be some time before Professor T is ready to ask Jitske his one question.
I've really enjoy this series and found this episode to be particularly good; more time is dedicated to the central mystery and the guest characters and less on the team member's various problems. Having a key character with Down's syndrome could easily have felt exploitative but Anke Verwaest's performance as Jitske was so delightful it never felt that way; the scenes between her and Koen De Bouw's Professor T, where they share various imagined moments that others can't see, were particularly charming. The case provided a reasonable number of suspects and a few nice twists before the ultimate reveal. This reveal isn't too surprising but that doesn't lessen the episode. Overall I thought this was a great episode.