Make a sinlge long doc out of many

I hope this is at least close to topical here:

The html content I want to change is in the form of a series of many
pages, now accessed from a Table Of Content where the headings leads
to a new page with that subject matter.

Where the index is a page with links to 
A B C  etc

and clicking them lead to new pages.

I want to put all the many single pages into one big page and of
course have the links still work.

I hoped to find out there is a way to at least semi automate the change.