In 1923 she published her first novel, Whose Body, which introduced Lord Peter Wimsey, her hero for fourteen volumes of novels and short stories. She also wrote four other novels in collaboration and two serial stories for broadcasting. Writing full time she rose to be the doyen of crime writers and in due course president of the Detection Club. Her work, carefully researched and widely varied, included poetry, the editing of collections with her erudite introductions on the genre, and the translating of the Tristan of Thomas from mediaeval French. She admired E C Bentley and G K Chesterton and numbered among her friends T S Eliot, Charles Williams and C S Lewis.
She married Arthur Fleming in 1926. In 1928 her father died at Christchurch in the Fens, his last parish, and she bought a cottage at Witham, Essex, to accommodate her mother. On the latter's death a year later she moved in herself and bought the house next door, No 22 Newland Street, to throw the two houses into one. There she worked until her death in 1957.
Gaudy Night was to be the culmination of the Wimsey saga, but her friend Muriel St Clare Byrne persuaded her to collaborate in putting Lord Peter on the stage in Busman's Honeymoon. The play was successfully launched in December 1936, and she gave up crime writing except for the book of the play and three short stories. With her new financial security she turned thankfully to the work for which she had been trained.
The stage fascinated her. She had already been asked to write a play, The Zeal of Thy House, for the Canterbury Festival. She followed this with six more, up to the Colchester Festival play, The Emperor Constantine in 1951. The most momentous was The Man Born to be King, written for broadcasting in children's hour at the request of the BBC. Her presentation of Christ's voice speaking modern English raised a storm of protest and revolutionised religious play-writing. Opposition stimulated her. She would never compromise where her art was concerned.
Her theology was traditionally Anglican with emphasis on doctrine. Every available moment of her time was spent writing, to the small hours of the morning. Letters, articles and essays streamed from her pen. The war led her to write Begin Here, followed by The Mind of the Maker, in which she compares the human with the Divine creator. She explored by-ways of knowledge, delighted in puzzles and enjoyed many a fight which she conducted with wit and good humour. Her formidable presence, magnificent brain and logical presentation put her in great demand as a lecturer. She worked with the Rev. Patrick McLaughlin at the St Anne's centre for Christian discourse and became in 1952 churchwarden of her London parish, St Thomas-cum-St Annes.
She found her culminating role after the war. Dante's writings had long intrigued her. Now she taught herself old Italian and made a translation in terza rima of The Divine Comedy unmatched for its popularity and the clarity of its notes. She also found time to finish her translation of the Song of Roland from the old French. But she unexpectedly died from heart failure on 17 December 1957 while engaged on Dante's third volume, Paradiso, and her friend Dr Barbara Reynolds completed her work. To the end she drove herself hard, living the philosophy she expressed in these words: