Once making headlines around the world, the story told in James Marsh's The Mercy is now more of a curious historical footnote.

The film begins in 1968 and follows British amateur sailor Donald Crowhurst (Colin Firth), who is trying to sell a navigational device he's designed at a boat show. While there, he sees British maritime hero Sir Francis Chichester (Simon McBurney) announce The Sunday Times Golden Globe Race, the first round-the-world yacht race.

Despite having barely left his home port of Teignmouth in Devon for the open ocean, and the objections of his wife Clare (Rachel Weisz), Donald decides to enter the race with an innovative trimaran yacht, complete with technical innovations of his own design including a buoyancy bag to prevent it capsizing in the feared Southern Ocean.

Aiming to do more than make his children proud, he hires a press agent, the slimy tabloid hack Rodney Hallworth (David Thewlis), to drum up publicity and bring in sponsors, hoping that completing his voyage will boost his business as well as his ego.

Although his prototype resembles the pricey vessels that now compete in today's global races, he struggles for funds and materials and faces a race against time to set off by the final day allowed under the rules.

Under pressure from his sponsors, led by caravan business owner Stanley Best (Ken Stott), who insists he offers his home and business as security, he departs with the boat's safety features incomplete, faulty technical equipment and shoddy provisions.

Inevitably, trouble strikes not long after Donald and his boat, the Teignmouth Electron, head into the Atlantic Ocean - as his inexperience and the unworthy vessel put him way behind schedule.
After the Electron is damaged in a storm, he realises he faces an impossible choice - return home to financial ruin or press on towards the feared Southern Ocean and likely death. His decision to do neither, and fake his progress, initially makes him a media star but has devastating consequences for his mental health.

The Mercy tells a remarkable story of the downside of British eccentricity and pluck - a tale of what happens when gentleman amateurs are not up to the task they set themselves but refuse to turn back. It's one that feels timely in the age of Brexit, but Marsh's film never really gets to the heart of its subject matter. The talented cast does their best, with Weisz particularly affecting as Clare, the devoted wife who finds herself reluctantly caught in a media storm of her husband's making, and Thewlis delighting in his character's amorality in pushing Donald towards media stardom.

One problem is the casting of Firth. His performance isn't a bad one, and in The Mercy's first act he succeeds in playing Donald as a decent but ambitious family man. However, the actor's innate charm means he fails to convince when his character goes off the rails. Even as the sailor finds himself mentally and literally adrift, one feels Firth's Donald is a long bath and a close shave away from returning to blameless bourgeois domesticity. This is no tale of heroic failure and one could've done with more edge from its lead.

As a result, what should be a dark examination of a bizarre but troubling moral tale, feels rather muted and uninterested in diving deeper into its subject's character flaws. That aside, The Mercy is a fascinating story competently if uninspiringly told.