SEQUEL

 

A sequel is a single book that continues another story written in another single book written at an earlier time.

 

For example:

ALICE IN WONDERLAND is the first Alice book.
It came out in 1865.
Alice falls down a rabbit hole and has adventures in
a very strange place.

 

THROUGH THE LOOKING GLASS was written many years later.
In this book, Alice's adventures continue as she walks
through a mirror (looking glass.)