Dead Mand and the Army of Frogs is slated to come out in August 2014. It follows the adventures of Denton (aka Dead Man) and Bran in Chicago as they face down spirits of all kinds.
Meanwhile, I have a short story, Dead Mand and the Lustful Spirit, set in the same world, and it's available as a free download. More
I'm working on a book set in the same world as Secrets and Ink. It's more spin-off than a sequel. The protagonists are Olly—Jem's friend from the previous book—and a troublesome redhead Olly keeps butting heads with. The book will probably come out in December.