I am a movie director and I just received the following movie plot. Could you help me answer this question? If not, let me know by writing "Not answerable". Plot title: Condemned to Live Movie plot: Professor Paul Kristan [Ralph Morgan] doesn't know that his mother was bitten by a vampire bat just before he was born. The doctor who delivered the baby some 40 years ago in a bat-infested cave within earshot of angry native drums in the darkest reaches of Africa, handed the bundle of joy to his colleague, Doctor Anders Bizet [Pedro de Cordoba], who raised the boy as his own son. Paul is now a grown man, beloved by everyone in the village because of his "goodness", and engaged to be married to the flower of the village, the beautiful Marguerite Mane [Maxine Doyle].Then the murders start. Three victims have been found lying in the caves, their throats torn open and the blood drained from their bodies. The cry goes up that this the work of a huge and loathsome vampire bat that kills during the dark of night and then carries the bodies into the caves. Only young David [Russell Gleason] cannot accept that there is a bat large enough to carry a human body. The good Professor isn't certain that it's a bat, but he is sure of one thing...the creature strikes only in the dark. Therefore, he suggests that everyone stay home after dusk and keep their lights burning.After bringing some roses to the good Professor, Marguerite meets David in the garden. David has been her friend since childhood, and he's in love with her. However, Marguerite is intent on marrying Professor Kristan because...well...he's so good. David attempts to convince Marquerite that what she feels is respect, admiration, and reverence but not love. Marquerite won't hear of it. She is honored that Professor Kristan (she's trying to learn to call him "Paul") has chosen her, and she intends to make the good Professor a good wife.That night, after seeing his last patient, Paul retires to his study to read his books by candlelight. The night gets darker, Paul falls asleep, and the candle burns out. When he awakens, it is dark outside. Suddenly, his face twists in pain. The good Professor has become the vampire. He climbs through the window of a sleeping... My question: who is hiding in a cave?
A:
a trio of explorers