The problem I always have with Agatha Christie films: They never tell how the conclusion was reached

Rating: 7/10 (30 November 2019)

That's the problem with this movie too! That's why a 7 instead of an 8 or even 9.
The detective never explains how he reached his conclusions at the end. That's a recurring problem with every movie or TV series based on Agatha Christie's novels, without exception!