THE SOLUTION

What's the solution to the mystifying song riddle? Well, the song is composed with only three notes: C, D and E. Each letter represents a dot, a dash or a space in Morse code. So, the C is a dot, the D is a dash, and the E is a space between letters. When you write out the names of the notes, you get this:

CDDECDEDECECDCEDEDDDECDDEDCEDCECECCCDECECDCEDDEDDDECDCEC

And when you add in breaks for the Es, indicating the end of a letter's code, it looks like this:

CDDE CDE DE CE CDCE DE DDDE CDDE DCE DCE CE CCCDE CE CDCE DDE DDDE CDCE C

And then assigning the dots and dashes of Morse code:

.-- .- - . .-. - --- .-- -. / -. . ...- . .-. / -- --- .-. .

Which spells:

WATERTOWN NEVER MORE

The key was in the Watertown library in the Collected Poems of Edgar Allan Poe.