The title derives from a line in the poem "XVI – (How clear, how lovely bright)", from More Poems, by A. E. Housman, a favourite poet of Dexter and Morse:

"Ensanguining the skies

How heavily it dies

Into the west away;

Past touch and sight and sound

Not further to be found,

How hopeless under ground

Falls the remorseful day."

Morse tries to solve the unsolved murder of Yvonne Harrison, as his health deteriorates.

Harrison, a nurse, has inspired romantic attachment in Morse during an earlier (and separate) illness, and he has written to her about it. She is a sharer of her favours; recipients, including her daughter's lover, are serially suspect.

His superintendent has found Morse's letter among crime-scene evidence but has sequestered it.

Morse dies of acute myocardial infarction; his last words are "Thank Lewis for me."

• 1999: London: Macmillan ISBN 0-333-76157-X, Pub date 15 September 1999, Hardback

This novel was adapted for the television series Inspector Morse as an episode of the same title "The Remorseful Day", the final episode of the series (fifth in Series 8) as well as of the novels.

• Bishop, David, The Complete Inspector Morse: From the Original Novels to the TV Series London: Reynolds & Hearn (2006) ISBN 1-905287-13-5