The Singing Detective S01E01 - Skin

What is the connection between the beady private eye crooning soft songs at the Laguna, and the disfigured man struggling for his sanity in a hospital bed?

Why does the small boy spy from the top of the tree, and who is the naked girl dragged out of the murky Thames? The clues are bloody and tangled, but the singing detective knows that the answers will eventually jump out of him as long as he keeps singing the right tunes.