name='Lord Brett']The novelisation of Magnum for Schieder is also very good (it was rereleased under the titles
Red File for Callan, and then
Callan when the film came out). James Mitchell wrote several other Callan novels, including a final one,
Bonfire Night just a couple of years ago, which you can probably still get on Amazon.
Interestingly,
Callan was predated by a series of excellent spy novels Mitchell wrote under the pen-name James Munro, featuring the character John Craig. The last of these,
The Innocent Bystanders, was a virtual re-write of
Magnum for Schneider, and was filmed in 1972 as
Innocent Bystanders. Stanley Baker played Craig (if I read the books now, it is Sir Stan I imagine), and I believe it was his last appearence in a British-made movie.
Those ITC compilations were great - I've still got a few of them from when they first came out.