On one of his walks through the park to take photos, Frank had come across something odd. First he thought he was hallucinating, but even after several attempts, one couple appeared in several photos, event hough he hadn't seen them in the viewfinder of his digital SLR camera. He managed to track them through the review of the last photo taken, growing more and more bewildered.
When they noticed him eventually, he decided to ask them directly. They invited him to a chat over coffee, and he accepted.
The two things he found out before his death were these: Sunlight does not bother vampires all that much, but they really don't show up in mirrors.