In December 2013, The Queen granted a posthumous royal pardon to Alan Turing.

The London-born mathematician had been prosecuted for homosexuality in 1952 - a criminal act at the time - and he undertook a treatment of chemical castration with oestrogen injections rather than serve time behind bars.

It was an undeservedly inglorious end for a brilliant man, who was instrumental in breaking the Enigma code and should have been feted by our battle-scarred nation as a hero.

Based on a biography by Andrew Hodges, The Imitation Game relives that race against time to decipher German communications and bring the Second World War to a swift conclusion.

Morten Tyldum's masterful drama neither shies away from Turing's homosexuality nor lingers on it, framing nail-biting events at Bletchley Park with the mathematician's 1951 arrest in Manchester.

"If you're not paying attention, you'll miss things," Turing teases us in voiceover.

Indeed, you'll miss impeccable production design, an unconventional yet touching romance, subterfuge and sterling performances including an Oscar-worthy portrayal of the socially awkward genius from Benedict Cumberbatch.

Alan Turing (Cumberbatch) sits in a police interrogation room with Detective Nock (Rory Kinnear), facing a charge of indecency with a 19-year-old unemployed man called Arnold Murray.

"I think Turing's hiding something," Nick informs his Superintendent (Steven Waddington), who is keen to wrap up the conviction.

In flashback, we witness Alan's arrival at Bletchley Park where Commander Denniston (Charles Dance) and Major General Stewart Menzies (Mark Strong) preside over a group of the country's keenest minds in the hope that one of them can break Enigma.

Hugh Alexander (Matthew Goode), John Cairncross (Allen Leech) and Peter Hilton (Matthew Beard) work alongside Turing, but he ploughs his own furrow and raises eyebrows by recruiting Joan Clarke (Keira Knightley) to the team.

She is a beautiful mind like Turing, inspiring him to greatness by observing, "Sometimes it is the people no one imagines anything of that do the things people never imagine."

Punctuated by school day scenes of the young Turing (Alex Lawther) and his first love, an older boy called Christopher (Jack Bannon), The Imitation Game is a beautifully crafted tribute to a prodigy, whose invaluable contribution to the war effort was unjustly besmirched by bigotry.

Cumberbatch is mesmerising, trampling over the egos of fellow code breakers without any concern for their feelings as he vows to solve "the most difficult problem in the world".

It's a tour-de-force portrayal, complemented by strong supporting performances from Knightley, Goode et al as the close-knit team who note, "God didn't win the war. We did."

The pivotal Eureka moment sets our pulses racing, heightened by Alexandre Desplat's exquisite orchestral score.

Director Tyldum navigates the fractured chronology with clarity and flair, ensuring that his heart-rending film doesn't itself become a perplexing puzzle.