What Changed Charlie Farthing? (also known as The Bananas Boat) is a riveting, comedy-laden 1970s film that brings together a stellar cast including Hayley Mills and Doug McClure. Set in a politically unstable Central American country, the movie draws upon themes of adventure, romance, and dark comedy that are guaranteed to keep the audience intrigued from start to finish.

The narrative centers on Charlie Farthing, played by the charismatic Doug McClure, known for his theatrical prowess and undeniable on-screen presence. Charlie is an opportunistic sailor who is gunning for some quick wealth. He's a free-spirited, playful individual, and his quirky attempts to exploit the political volatility of the country to his advantage serve as a main driving force in the plot.

Charlie hatches an audacious plot to retrieve a stash of buried treasure but soon finds himself embroiled in the local political tussle. His lofty plans, however, hit a snag when he finds out that the exact location of the treasure is within a cemetery that is currently under the regime's watchful eye.

Hence, to succeed in his extravagant quest, Charlie poses as a temporary gravedigger to access the cemetery. His adventure takes an interesting turn when he encounters the ever-enchanting Hayley Mills, who plays the role of Jenny, an alms-house nurse. Peterson creates an affectionate, morally tethered, and astutely discreet character in Jenny. Her performance stands as an applaudable contrast to the rest of the film's swashbuckling nature.

Despite existing within a comic adventure, Jenny’s character is not devoid of complexity. As an altruistic character providing care for the old and infirm at the local hospital, Jenny is innately sympathetic and skeptical of Charlie's true intentions, leading to an interesting dynamic between the lead characters.

The movie takes an engaging turn when Jenny becomes an unexpected participant in Charlie's audacious treasure-retrieval plan. The chemistry between Hayley Mills and Doug McClure is at its most dynamic throughout these scenes, and their unpredictable relationship keeps the audiences guessing to the end.

Breathing life into these characters is the skillful direction of Sidney Hayers, known for his remarkable knack for creating believable characters and intriguing storylines. Hayers successfully manages not only to paint a vivid picture of the socio-political landscape of the country but also to extract the potential from the script, steering the lead characters through amusing scenarios and heart-wrenching moments.

The film's setting also plays a significant role in enhancing its appeal. Flanked by a rich backdrop of tropical landscapes, the Central American setting imbues the screenplay with a sense of captivating exoticism. The vibrancy of the local culture and the continuous political strife provide a distinctive texture that effectively accentuates the various elements of the plot.

Another remarkable aspect of 'What Changed Charlie Farthing?' is its script, expertly penned by Trevor Peacock. The comedic timing paired with the dark undertones keeps the audience glued to their seats. The dialogue is witty yet poignant, and the humorous scenes are complemented by moments of unexpected pathos, all while stirring suspense about Charlie's fate.

The movie is titled 'What Changed Charlie Farthing?' hinting at a profound transformation within the main protagonist. As Charlie's journey unfolds, the viewers get to witness the shift in his character brought about by his experiences and interactions with Jenny and the other colorful characters he encounters.

In conclusion, 'What Changed Charlie Farthing?' is an entertaining, unconventional adventure-comedy set against a volatile backdrop. It's a movie that balances comedy, romance, and an undercurrent of political tension, that tightly knits the narrative together, compelling audiences to join in on this unconventional treasure hunt. The movie's charm lies not just in the hilarious hijinks and daring quests of its protagonist but in the emotional journey and personal transformation underlying it. The film promises an unforgettable journey filled with laughter, suspense, and a few hearty moments along the way.