Deadly Reunion

From Author Wars - https://authorwars.com/publications/deadly-reunion-143831.html

Overview:

Title: Deadly Reunion
Author: Terrance Dicks, Barry Letts
Year: 2003
ISBN-10: 0563486104
Publisher: BBC Books
Price: £5.99
Pages: 287
Binding: Paperback
Type: Novel
Title Reference: Deadly Reunion
Notes: USA $6.95, Canada $8.99.
Cover design by Black Sheep.
"About the Authors" is uncredited but the Barry Letts section is written in the 1st person, while the Terrance Dicks one is written in the 3rd person, although in such a way that you suspect only the author would write with such honesty.
Month from Wikipedia.