Les Misérables

Les Misérables was a French novel written by Victor Hugo. (PROSE: Just War)

The book was originally going to be a comedy, but the entire plot was changed after Hugo was brought to the Catacombs beneath Paris by the Fourth Doctor, which nearly gave the writer a heart attack. (COMIC: The Forgotten) Hugo wrote it in Guernsey. The Doctor told him to change the title, but he wouldn't listen. (PROSE: Just War)

A play based on the novel was performed in the United States many times, but also featured in England. The Eleventh Doctor suggested the necrotist Monos should go see it while he was in London. (COMIC: Sticks and Stones)

The Twelfth Doctor once described Les Misérables as one of several things he'd "never seen", which was usually because he'd "chosen not to see them". He claimed that "[e]ven [his] incredibly long life [was] too short for Les Misérables." (TV: In the Forest of the Night)

Behind the scenes
Although In the Forest of the Night does not go into detail as to what version of Les Misérables the Twelfth Doctor is talking about, the context of Les Misérables being one of the things the Doctor has chosen not to see rather than read or be shown implies he's talking about the stage adaptation. Indeed, British audiences at the time the episode aired would be familiar with the play, which opened in the West End of London in 1985, and continued to be performed there. There was also a film version of the musical released in 2012 that the Doctor could be referring to.