Choose Your Own Chemical Adventure

You are standing in front of a run-down house in George Street, Manchester. It is summer time and the sun is shining. You are in a good mood.

Mounting the steps, you walk up to the front door. Whilst its green paint is beginning to flake, the number twenty-five is still clearly visible. Next to the door there is a bell. Underneath this a plate bears the inscription "Reverend W. Johns".

What do you do?