I am currently re-watching many past Poirot episodes, but out of all the sixty-plus instalments, this has to be my favourite. With imaginative skill, director Paul Unwin takes one of Agatha Christie's more sombre, poignant books and turns it into a visual masterpiece. This is a truly astonishing work; making it all the more unfortunate it will never be shown theatrically.

However, we must be thankful that ITV saw fit to turn their Poirot adaptations around, losing the playful humour of the previous episodes by injecting a tangible sense of fear, menace and sadness. This feature-length story marks a change in tone for the series, and benefits greatly from it. From the opening scene we can see a marked difference. The warm Poirot theme tune has gone (although listen out for a variation on it at the end), replaced by the haunting melody of Erik Satie's First Gnossienne. Music plays a large role in this film, introducing a reflective atmosphere, which proves very appropriate to the cleverly woven plot.

The story is told in flashback - a dangerous technique that can usually distort and hinder rather than help a plot unfold, but here is used to produce an unexpectedly powerful effect. When a young woman, Lucy Crale, returns to England on discovery that her real mother was hanged for killing her father, she commissions Hercule Poirot to look over the case. Part of her motive for this commission is the fact that, at the age of 21, she was given a letter, written by her mother 14 years previously, insisting that she was innocent and was being hanged for a crime she did not commit. Lucy wishes to see the facts for herself, and to put her mind at rest. So Poirot, in his role as a neutral assessor, pays a visit to each of the five adults present at the time of Mr Crale's death.

David Suchet works genius with Poirot as both a character and a pivotal plot device. However, the true star of this sumptuous film is the gorgeous cinematography. The clever mixing of colours - a warm, lush look for the flashbacks set in sunny Devon, and a cold hard look to the present day. Kevin Elyot's screenplay wonderfully captures the darker feel of the novel, and although it does introduce a new homosexual subplot that wasn't so present in Christie's text, it manages to thread the many layers of the story together with expert competence.

Although there are around four new episodes of this series every two years, the quality of this adaptation and its direction has never been matched. Although many of the mysteries are miniature masterpieces, none seem to carry such a wealth of talent as this exceptional piece of drama. I cannot recommend it highly enough.