The central theme in "The Masque of the Red Death" is the inevitable, or perhaps more accurately, the inescapable nature, of death. Prospero and his companions attempt to shut themselves off from the rest of the world in an attempt to avoid the horrible plague (the "red death") that is ravaging the countryside.
You already answered the question. The claim is you shouldn’t talk to strangers. The support theme shows that in the evidence because little red riding was too trusting of the wolf, the “stranger” she ended up putting her grandmother and herself in danger.
