Michael Dahl 
Maze Monster [PDF ebook] 

Two friends decide to sneak into an abandoned science laboratory to explore, only to find that the lab isn’t empty after all. Strange security guards patrol the grounds. Even stranger, almost all of the doors inside are locked. And they keep hearing an eerie, chattering sound around every corner. When they try to leave, they realize that the place is more like a labyrinth than a laboratory — and like most labyrinths, this maze has a monster waiting at the finish line . . .