Getting a Perfect Score

Hint 1 of 20:

You only need six different locations to solve this mystery.

Hint 2 of 20:

In fact, you don't even have to visit one of those locations yourself.

Hint 3 of 20:

The Irregulars can give you the sixth piece of the puzzle.  Here's the
summary of the case:

Hint 4 of 20:

1) Guy Clarendon was 7000 pounds in debt.