George Bernard Shaw's "Pygmalion" begins with "torrents of heavy summer rain" falling on a London street scene. A group of pedestrians has taken shelter near a church as people scramble about looking for taxies.
Shaw uses this setting to bring together all the main characters of his play in the first scene. Freddy, who will become Liza's lover, is looking for a taxi for his mother and sister. Liza is trying to sell flowers to the people waiting for taxies. Colonel Pickering, who is among those waiting for a taxi, buys some flowers from Liza. Higgins is standing nearby, taking notes on Liza's interesting way of speaking English.
If not for the rain, all these people would not likely be found in the same place. Shaw uses the rain as a plot device to introduce his characters and begin his plot.