Humanitarian — As a young man Casement worked and travelled in Africa; in all he was to spend a third of his life there. In 1892 he joined the British Consular Service, representing the United Kingdom as consul in Mozambique, Angola, and the Congo. The "Casement Report", published 1904, brought him to international attention. This eye-witness account highlighted the abuse of native forced labour in the Congo Free State, then the personal fief of King Leopold of the Belgians. The regime described was horrific: punishments abounded, from chaining and whipping to casual execution for failure to bring in the day's quota of rubber. The report scandalized the Great Powers, and resulted in a reformation of Belgian rule in the Congo.

In 1905, in recognition of this work, Casement was appointed CMG (Companion of the Military Order of St Michael and St George – the traditional British order for colonial diplomats). A later exposé, this time of labour conditions suffered by the Putumayo Indians in Brazil - "slavery without law", he called it – further enhanced his humanitarian reputation, and he was appointed KCMG (a Knight in the above Military Order).

Nationalist — He retired from the Consular Service in 1913, aged 49. He had been from youth a nationalist: now he devoted his energies to Ireland. He was influential in forming the Irish Volunteers in 1913 and served on its Provisional Committee. July the next year, he helped finance the Howth gun-running (by which the Volunteers armed themselves by an illegal importation of Mauser rifles). That same month he sailed to the US to raise funds for the Volunteers.

Germany — In the meantime, World War One broke out. Casement conceived an extraordinary plan to recruit in Germany from amongst the Irish prisoners-of-war (captured soldiers of the British Army) an Irish Brigade that would sail to Ireland and fight for Irish independence.

With this in mind he took ship in October 1914 for Germany. The plan was a spectacular failure. Casement addressed thousands in the prison camps: only a handful signed up for his Brigade. The German Government in 1916 agreed to supply arms for the intended uprising in Ireland, to the tune of 20,000 rifles and 10 machine guns: a fraction of the weaponry Casement had hoped for. In April 1916 Casement decided to return to Ireland, though whether in hopes of leading the Rising or of calling it off, is not clear.

Arms Shipment — The arms were carried in a German steamer disguised as a Norwegian cargo vessel. This vessel actually managed to evade the Royal Navy and come to the Kerry coast, on the south-west of Ireland. But no signal lights showed from the shore, no reception was waiting – it was later learned that the three Irish Volunteers detailed to receive the arms had drowned earlier that day when their car drove off a nearby pier. The arms-ship stood out to sea, where it was intercepted by a Royal Navy patrol.

Meanwhile Casement had travelled by U-boat. Arriving at the rendezvous off the Kerry coast, and finding no arms-ship waiting, Casement decided to venture ashore. Already in ill health, the two miles in a dingy exhausted him entirely: he collapsed where he landed, and was shortly afterwards arrested by the local constabulary. This was the Good Friday before the Easter Rising, 21st April 1916.

Trial — Casement was immediately spirited to England. He was charged with treason, and, appropriately for such a charge, incarcerated in the Tower of London. At his trial he gave an eloquent and unrepentant speech from the dock:

Casement was found guilty, and sentenced to be hanged.

Appeals — Casement was the only leader of the 1916 Rising to have any reputation outside Ireland. Appeals were mounted both in England and the US for clemency. To thwart these pleas, the British authorities discreetly circulated extracts from Casement's private diaries. These "Black Diaries" betrayed, in the words of poet Alfred Noyes, 1916, "the lowest depths that human degradation has ever touched. Page after page of his diary would be an insult to a pig's trough to let the foul record touch it." In short, they revealed Casement to have been homosexual.

Black Diaries — All Casement's diaries, both the "Black" and the more regular "White", reveal a man curiously obsessed with minor details: tips given to waiters, alms given to beggars, bus and taxi fares, number of cigarettes smoked. In the case of the "Black Diaries" the obsession extends to size.

But what leaps from the page is the excitement of seeing, of contact:

And there is, of course, the inevitable but succinct sadness:

Irish nationalists vehemently disputed the diaries' authenticity. It seemed obvious they were a British forgery designed to blacken a good man's reputation. It is possible of course to imagine a Crown employee sucking upon his office pen and inventing these titillating details: but it has never been likely. Forensic tests of the diaries in 2002 resulted in the "unequivocal and confident" conclusion that the diaries are genuine. But die-hard "Casementalists" still abound. Part of the reluctance to accept the diaries is a lingering anti-homosexual feeling; partly it's an incomprehension that an Irishman could have sex three times in a day, with three separate partners, and still want more:

Death — Casement was hanged at Pentonville Prison in London on 3 August 1916 – almost three months after public opinion, both at home and abroad, had procured the end of executions in Dublin.

The hangman later recalled: "He appeared to me the bravest man it fell to my unhappy lot to execute." In 1965, his remains were repatriated to Ireland. An estimated half million people filed past the coffin. He was buried with full military honours in the Republican plot in Glasnevin Cemetery, Dublin.

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