For director Sean Ellis, location shooting, period detail and authenticity were crucial in making Anthropoid, his beautifully stylised but slow-burn Second World War thriller set in 1940s Prague. The film tells the extraordinary, true story of the mission undertaken by the Czech resistance to assassinate SS officer, Reinhard Heydrich - code-named Operation Anthropoid, for reasons that are never explained.

Known as "The Butcher of Prague," Heydrich was the Reich's third in command after Hitler and Himmler and leader of the occupying Nazi forces in Czechoslovakia.

He was also one of the main architects of the Final Solution.

The film focuses on two soldiers, Jan Kubiš (Jamie Dornan) and Josef Gabcík (Cillian Murphy) who parachute into their occupied homeland in December 1941, having been sent by the London-based Czech government-in-exile to carry out the task.

They seek assistance from the depleted Czech resistance whose leaders (including Toby Jones) are initially reticent, fearing the consequences of such a mission.

Failure or success, they are acutely aware that the fallout will be severe: excessive reprisals by the Nazis against the Czech population and almost inevitable death for the paratroopers.

Kubiš and Gabcík move into the home of a resistance member and her family and soon two rather clichéd love interests emerge.

Kubiš, the more sensitive of the two men, is driven by the possibility of a future with Marie (Charlotte Le Bon).

Gabcík displays a determined, cold, steely resolve and is more about "getting the job done" but eventually he too softens, falling for Lenka, played by Ana Geislerová.

The men's characters are credible and neatly contrasted - at one point, Kubiš's vulnerability surfaces to the extent that he panics and there is an excruciating moment where the camera rests on his trembling trigger finger.

With limited intelligence and even less equipment, they begin planning the assassination. The raw and oppressive feel of a city under occupation is palpable but the film's first half is too long and at times, dull.

However, once the assassination attempt is under way, followed by a manhunt, the pace picks up and tensions spiral - the handheld camerawork adding immediacy to the action.

The film catapults to a shattering shoot-out finale in a cathedral, where the soldiers and other members of the underground have taken refuge. The exterior sequences for the church were shot at the Saint Cyril and Methodius Cathedral in Prague, where the actual confrontation between the partisans and the Nazis took place. If it feels a little protracted this might be Ellis acknowledging the lengthy time of the battle - the Germans were held off for six hours.

During the siege there is a crescendo when Gabcík's martyrdom is represented in Christ-like imagery. Its significance is not lost.

The operation came at a high cost - Nazi retaliation was brutal with 5,000 men, women and children killed in reprisals.