Kerry Greenwood 
Stormbringer lll: Ravens Rising 

After bringing down the Lightning Nest, the heroes of THE RAT AND THE RAVEN have returned to the University, only to find it deserted and the gates locked. Dismas, who can break any lock, opens the outer door and they gain entry, but then they find that they are locked in and now not even Dismas can open the doors. Who is Emmanuel and how is it that he seems able to control their thoughts? Locked in the tower, the Ravens must fight to defend everything that is most precious their very humanity is at risk. Emmanuel wants desperately to become human and needs to overwhelm and inhabit them to ensure his own survival.