I recommend reading each of Anne Perry's series of detective novels in the order of publication; each series follows the adventures of the main characters chronologically; each book builds on and refers to events of the previous books within its series. If you read them out of order, some of the surprises will be spoiled. For this reason, I have carefully listed them in order below. I list Monk before Pitt, even though the Pitt series was started first, because the Pitt series deals with the earlier days of Queen Victoria's reign. What I enjoy most in Perry's novels is the unfolding of the historical background in which she sets her stories, particularly the development of the women's rights movement. It is also interesting to observe Perry's growth as a writer.

The Face of a Stranger; Anne Perry   First in the William Monk series.
Amazon.com
 
A Dangerous Mourning; Anne Perry   Second in the William Monk series.
Amazon.com
 
Defend and Betray; Anne Perry   Third in the William Monk series.
Amazon.com   Mass Market Paperback, 1994
 
A Sudden, Fearful Death; Anne Perry   Fourth in the William Monk series.
Amazon.com   Mass Market Paperback, 1994
Amazon.com   Audio Cassette, 1995   Narrated by Terrence Hardiman
 
The Sins of the Wolf; Anne Perry   Fifth in the William Monk series.
Amazon.com   Mass Market Paperback, 1995
Amazon.com   (Thorndike Large Print Cloak and Dagger Series) Hardcover, 1994   Special Order
 
Cain His Brother; Anne Perry   Sixth in the William Monk series.
Amazon.com   Hardcover, 1995
Amazon.com   Mass Market Paperback, 1996
Amazon.com   (Thorndike Large Print Cloak and Dagger Series) Hardcover, 1996
Amazon.com   (abridged) Audio Cassette, 1997   Narrated by Simon Jones
 
Weighed in the Balance; Anne Perry   Seventh in the William Monk series.
Amazon.com   Mass Market Paperback, 1997
Amazon.com   (Thorndike Large Print Cloak and Dagger Series) Hardcover, 1997
Amazon.com   Audio Casette, 1996   Narrated by Simon Jones
 
The Silent Cry; Anne Perry   Eighth in the William Monk series.
Amazon.com   Hardcover, 1997   Usually ships in 2-3 days
Amazon.com   Hardcover, 1998   Special Order
Amazon.com   Paperback, 1998   Special Order
Amazon.com   Mass Market Paperback, 1998
Amazon.com   (Thorndike Large Print Basic Series) Hardcover, 1998
Amazon.com   (abridged) Audio Casette, 1997   Narrated by Simon Jones
 
A Breach of Promise; Anne Perry   Ninth in the William Monk series.
Amazon.com   Hardcover, 1998
Amazon.com   Mass Market Paperback, 1999
Amazon.com   (Thorndike Large Print Basic Series) Hardcover, 1998
Amazon.com   (abridged) Audio Casette, 1998   Narrated by Simon Jones
Amazon.com   (unabridged) Audio Cassette, 1999   Narrated by Terrence Hardiman
 
The Twisted Root; Anne Perry   Tenth in the William Monk series.
Amazon.com   Hardcover, 1999
Amazon.com   (Random House Large Print) Hardcover, 1999
Amazon.com   (abridged) Audio Casette, 1999   Narrated by Simon Jones
Amazon.com   Paperback, 2000
 
Slaves of Obsession; Anne Perry   Eleventh in the William Monk series.
Amazon.com   Hardcover, 2000
Amazon.com   (abridged) Audio Casette, 2000   Narrated by Simon Jones
 
Funeral in Blue; Anne Perry   Twelfth in the William Monk series.
Amazon.com   Hardcover, October 2, 2001
 

More by Anne Perry

Anne Perry's Historical Novel Series Featuring Detective Charlotte and Detective Thomas Pitt
A Dish Taken Cold; Anne Perry
Sounds Like Murder Series (unabridged) Audio Cassette, 1999.   Narrated by Claudia Besso.
"Days before the French Revolution, Celie's baby dies mysteriously in the care of a friend. Now, as Celie comes to grips with the death of her child, she also learns the true meaning of revenge."   ~ Borders.com
 
Amazon.com
 
Bluebonnet Books 2; Anne Perry
 
Bluebonnet Books: Activities for 1993; Anne Perry
 
Killer Books: A Reader's Guide to Exploring the Popular World of Mystery and Suspense; Anne Perry, Jean Swanson, et al.
Amazon.com   Paperback, 1998
 
Malice Domestic: An Anthology of Original Traditional Mystery Stories; Anne Perry et al.
Amazon.com   Mass Market Paperback, 1997
 
Mystery's Most Wanted : The Year's Finest Crime and Mystery Stories; Anne Perry et al.
Amazon.com     Mass Market Paperback, 1997
 
The Anne Perry Boxed Set; Anne Perry
Amazon.com   (abridged) Audio Casette, 2000   Narrated by David McCallum