Spoiler Alert: Although they are being closely observed by detectives to make sure they did not communicate the secret number to anyone, one of the suspects was somehow able to convey it to another person at a wine tasting event. This situation is quite contrived, and I can think of many simpler ways they could have achieved it, but it is cute that the number was conveyed in base 3 using the selection of white, red and rosé wines as the digits.

Thanks to Johan Richter who wrote to let me know about Aird's use of mathematics.