This book is one of my absolute favorites. Combining Sci-fi, alternate reality, artificial intelligence, natural intelligence , inner and outer worlds plus a bit of a romance angle.
Cassiopia's father has gone missing, and she and Scott Markman are trying to find him with the help of a very special prototype AI robot that her father has, but shouldn't have. Fortunately Cassiopia is the AI Scientist who programmed the Tel (the robot), and the threesome are able to work together to find the missing professor.
Scott is a consultant to law enforcement in an unofficial official way, or an official unofficial way, but he's not your typical Fed or Local law enforcement type. He's Mr. Action for sure, but with an eastern philosophy point of view. Cassiopia is all geek, logic and finding her dad, but there's "something" that sparks between these two characters.
The professor is the classic absentminded genius, once he does show up, and the Tel - the robot - is AWESOME.
The Empty Door of the title is the mystery, with lower case m and upper case M both. There is another world/s on the other side of the door that goes nowhere. It leads nowhere, but when a person steps through it, it takes that person someplace else - somewhere different. And it's an amazing journey with Cassiopia and Scott as they search the 'there' trying to find her father.
Not your average book. Not your average story line. But if you like the sounds of what I have described I hope you would like this book.
It's a favorite among favorites for me and I am ever so thankful that the author created this and that he has written not just this book but a continuing series of sequels with the same characters and theme/world/feeling.