I found this story in Judith Flanders's The Invention of Murder.
In the 19th century, most successful novels were turned into plays. The theatre was HUGE in Victorian Britain, and you could get many play variations on the same book at the same time. There could be stage readings done by the author, it could be turned into a burlesque-y vaudeville-style show for the lower classes, a straightforward drama for the middle classes, an opera for the upper classes, or a melodrama that
no one in their right mind everyone could enjoy.
In 1815, Sir Walter Scott (he of Ivanhoe, Rob Roy and the Waverly novels fame) wrote a historical romance called Guy Mannering. What happens in Guy Mannering isn't really important, except that you need to understand that it is a serious novel about serious gothic-y things set up in the Scottish highlands. This is not a frivolous or comedic book.
So since Walter Scott was kind of a big deal, everyone and their mums was turning his novels into stage productions. In 1829, one company turned Guy Mannering into a melodrama, a style which was "regularly interspersed with comedy, mime, spectacle, song and dance" (33). So, you know, stuff that's really appropriate for heavy subject matter. I've always thought, "If only The Godfather had a bit more mime…"
During their adaptation, "a character is lost on a storm-racked Scottish heath, when suddenly: [these are verbatim lines spoken by the character] 'Ha! What do I see on this lonely heath? A Piano? Who could be lonely with that? The moon will shortly rise and light me from this unhallowed place; so, to console myself, I will sing one of Julia's favourite melodies.' And he does" (33).
You guys. That is the WORST segue into a musical number I have ever heard in my life. That scene is supposed to be really tense and horrible for him. This is not the time to Michelle Pfeiffer it up on a piano.