The Mercy: Half-starved Colin Firth in a half-finished movie

All at sea doesn't begin to cover it. It defies comprehension that a director as accomplished as James Marsh (whose credits include Oscar-winning documentary Man on Wire and the Stephen Hawking biopic The Theory of Everything) was involved in this woefully misconceived (and suspiciously long-delayed) period drama.

The story of Donald Crowhurst has, to date, inspired plays, novels, music and even poetry, but it always felt like a hard sell as a narrative feature. So it proves.

On October 31st, 1968, Crowhurst, a businessman and amateur sailor, set off in the Sunday Times Golden Globe Race, a competition to be the first person to sail nonstop and single-handedly around the world. His 35ft boat, built from his own design, was unsuitable and unfinished, and as he fell farther and farther behind, he was faced with an impossible choice: return home to humiliation and financial ruin, or die at sea.

In July 1969 his boat, Teignmouth Electron, was found in the Sargasso Sea with faked log books, increasingly unhinged diary entries, and no captain.

In common with its tragic protagonist, The Mercy has nowhere to go. Crowhurst, as essayed by Colin Firth, sets out on a plainly doomed mission which turns out to be a plainly doomed mission.

There's a good deal of bobbing about with a fretful, half-starved Firth; back on land, Rachel Weisz, playing Crowhurst's unfortunate wife, provides a drier variation of restiveness. Frown lines, ahoy. Even these seasoned, capable actors and Motorcycle Diaries DP Eric Gautier's heritage-handsome cinematography, can't convince us that we're watching a proper movie.

Too often, The Mercy feels like a cruel meta-joke, an abandoned misadventure about an abandoned misadventure. Crowhurst's mysterious final days on the waves remain just that. The film fails to convey even such basic information as the gap between where the ill-fated circumnavigator claims to be and where he actually is.

Likeable players, including Ken Stott and David Thewlis, pop up in underdeveloped supporting roles to no avail. Abandon ship.