There has to be a way to get out of this situation and get his book.
If you cast a spell at him, he fries you, a spell at the dragon, he hits you with a spell.
Then, you get an idea. The mass transform spell. You could hit both him and the dragon with the spell. However, the problem is you would also be hit by the spell, and thus effected as well. Yet, it could save your butt here. However, if you can get to your own book first and recover from the spell, then you could win.
You try to think of an animal as you cast the spell and hope that the dragon isn't immune to magic.
"Mass Transform!" You shout.
"What?" The man responds.
There are three poofs, and you feel yourself fall to the ground as you're much smaller. You quickly crawl out from your oversized clothing. The animal you had chosen was a mouse, because well, they're small and harmless. You turn to where the dragon was, and there is another mouse there, and you are unable to see where the man went, but he is probaly somewhere around where his clothing hit the ground.
You jump into the Book of Beast and look at it, looking for the next spell. What can catch a mouse?
"Shape!" you squeek the command word, as another cloud of smoke surrounds you. This time when it clears, you're a cat. The dragon is closet, so you turn around and pounce at it, it still seems to be disoriented from the transformation, and you easily kill it.
You've just slain a dragon. True it was a mouse at the time, but that still probaly makes you some kind of hero.
However, you don't have time for that, as the man may try to cast spells from his own book. You run as fast as you can for where his clothes are, but then see a large poof of smoke.
You skid to a hault, now standing in front of another dragon. The man transformed himself.
"Meow." You say which roughtly transforms to 'Crap.'
The man lets out a roar, and begins to inhale.