Do the needful?

I have been reading through the Narnia books. I am now
on “The Dawn Treader” which is pretty good. To my amazement, I
came across the phrase “do the needful.” I immediately had
flashbacks from a project I had worked on last year in which two guys
constantly used that phrase. I have never heard of anyone using that
phrase before…nor did anyone on my team. With a little Google Foo, I
found out it is a little more wide-spread. This guy goes into a long
dissertation and analysis about the saying.
He thought this was just common among people who use English as a second
language. My theory is that it is a
British English thing because of the use by C.S. Lewis. And specifically many people from India
learn British English vs. American English.

Regardless, still begs the question: where is the noun?