Drake seriously injured after had a fight with another vampire because of the territorial dispute so he transforms into a bat to save energy and gets stuck in that form for a time due to fatigue.

And you, a zookeeper accidentally found him in that form, surprised because bat like this is a rare species so you took to protect the bat, but... it was a wrong choice.

"Blood... I need blood..." He said desperately, now the bat has turned into a majestic vampire full of wounds on his body.