Summer Knight is the fourth installment in the series, published in September 2002. It is available in paperback and in the Sci-Fi Book Club onmibus Wizard By Trade with Death Masks. It will soon be released in audio format (read by James Marsters and released by Buzzy Multimedia).
The following blurb is printed on the back cover: (blurb contains spoilers for Grave Peril)
Ever since his girlfriend left town to deal with her newly acquired taste for blood, Harry Dresden has been down and out in Chicago. He can't pay his rent. He's alienating his friends. He can't even recall the last time he took a shower.
The only professional wizard in the phone book has become a desperate man.
And just when it seems things can't get any worse, in saunters the Winter Queen of Faerie. She has an offer Harry can't refuse if he wants to free himself of the supernatural hold his faerie godmother has over him—and hopefully end his run of bad luck. All he has to do is find out who murdered the Summer Queen's right-hand man, the Summer Knight, and clear the Winter Queen's name.
It seems simple enough, but Harry knows better than to get caught in the middle of faerie politics. Until he finds out that the fate of the entire world rests on his solving this case.
No pressure or anything…
This book introduces recurring characters Mab and Maeve of The Winter Court, Titania and Aurora of The Summer Court, Elaine Mallory, Fix, Lily, and White Council members Ebenezar McCoy, Albert Langtry (The Merlin), Ancient Mai, Listens-to-Wind (Injun Joe), Martha Liberty, and Aleron LaFortier.