The "Agatha Christie indult" is a nickname applied to the permission granted in 1971 by Pope Paul VI for the use of the Tridentine Mass

Tridentine Mass

The Tridentine Mass is the form of the Roman Rite Mass contained in the typical editions of the Roman Missal that were published from 1570 to 1962. It was the most widely celebrated Mass liturgy in the world until the introduction of the Mass of Paul VI in December 1969...

 in England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 and Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

. "Indult" is a term from Catholic canon law referring to a permission to do something that would otherwise be forbidden.

Following the introduction of the Mass of Paul VI

Mass of Paul VI

The Mass of Pope Paul VI is the liturgy of the Catholic Mass of the Roman Rite promulgated by Paul VI in 1969, after the Second Vatican Council...

 to replace the former rite in 1969-1970, a petition was sent to the Pope asking that the Tridentine Rite be allowed to survive in the dioceses of England and Wales. The petition noted the exceptional artistic and cultural heritage of the Tridentine liturgy, and was signed by many prominent Catholic and non-Catholic figures in British society, including Robert Graves

Robert Graves

Robert von Ranke Graves 24 July 1895 – 7 December 1985 was an English poet, translator and novelist. During his long life he produced more than 140 works...

, Professor Sir Maurice Bowra

Maurice Bowra

Sir Cecil Maurice Bowra was an English classical scholar and academic, known for his wit. He was Warden of Wadham College, Oxford, from 1938 to 1970, and served as Vice-Chancellor of the University of Oxford from 1951 to 1954.-Birth and boyhood:...

, Iris Murdoch

Iris Murdoch

Dame Iris Murdoch DBE was an Irish-born British author and philosopher, best known for her novels about political and social questions of good and evil, sexual relationships, morality, and the power of the unconscious...

, Sir Kenneth Clark

Kenneth Clark

Kenneth McKenzie Clark, Baron Clark, OM, CH, KCB, FBA was a British author, museum director, broadcaster, and one of the best-known art historians of his generation...

, Cecil Day Lewis, Dame Joan Sutherland

Joan Sutherland

Dame Joan Alston Sutherland, OM, AC, DBE was an Australian dramatic coloratura soprano noted for her contribution to the renaissance of the bel canto repertoire from the late 1950s through to the 1980s....

, Nancy Mitford

Nancy Mitford

Nancy Freeman-Mitford, CBE , styled The Hon. Nancy Mitford before her marriage and The Hon. Mrs Peter Rodd thereafter, was an English novelist and biographer, one of the Bright Young People on the London social scene in the inter-war years...

, two Anglican bishops, Graham Greene

Graham Greene

Henry Graham Greene, OM, CH was an English author, playwright and literary critic. His works explore the ambivalent moral and political issues of the modern world...

, Philip Toynbee

Philip Toynbee

Theodore Philip Toynbee was a British writer and communist. He wrote experimental novels, and distinctive verse novels, one of which was an epic called Pantaloon, a work in several volumes, only some of which are published...

, Yehudi Menuhin

Yehudi Menuhin

Yehudi Menuhin, Baron Menuhin, OM, KBE was a Russian Jewish American violinist and conductor who spent most of his performing career in the United Kingdom. He was born to Russian Jewish parents in the United States, but became a citizen of Switzerland in 1970, and of the United Kingdom in 1985...

 - and the crime novelist Agatha Christie

Agatha Christie

Dame Agatha Christie DBE was a British crime writer of novels, short stories, and plays. She also wrote romances under the name Mary Westmacott, but she is best remembered for her 66 detective novels and 14 short story collections , and her successful West End plays.According to...

. Cardinal John Heenan, the leader of English and Welsh Catholics, subsequently approached Pope Paul VI and asked that use of the Tridentine Mass be permitted.

On 5 November 1971, the Pope granted the request. Between then and the granting of the worldwide "universal indult" in 1984, the bishops of England and Wales were authorized to grant permission for the occasional celebration of Mass in the old form, with the modifications introduced in 1965 and 1967.

English Catholics had a particular attachment to the Tridentine Mass, as the Mass which had been celebrated by the English martyrs of the Reformation

English Reformation

The English Reformation was the series of events in 16th-century England by which the Church of England broke away from the authority of the Pope and the Roman Catholic Church....

and by priests in the years in which Catholicism had been subjected to sometimes severe persecution.

The indult acquired its nickname by virtue of a story told about the Pope's acceptance of the petition:

The story is that Pope Paul read through the letter in silence then suddenly exclaimed, "Ah, Agatha Christie!" and then signed it. He must have been one of her fans. The English Indult of 1971 was granted and thus was saved the old Mass. Ever since it has been known informally as the Agatha Christie indult.

The text of the petition and of the response of the Sacred Congregation for Divine Worship to Cardinal Heenan's request are available online here. (The link is broken)