What did Mrs. Turner see while walking alone in the street one night?

One night, Mrs. Turner, an old widow, was walking along a dark London street. She was carrying her handbag in one hand and a plastic bag in the other. There was nobody else in the street except two youths. They were standing in a dark shop doorway. One of them was very tall with fair hair, the other was short and fat with a beard and moustache.
   The youths waited for a few moments, and then ran quickly and quietly towards Mrs. Turner. The tall youth held her from behind while the other youth tried to snatch her handbag.
   Suddenly, Mrs. Turner threw the tall youth over her shoulder. He crashed into the other youth and they both landed on the ground. Without speaking, Mrs. Turner struck both of them on the head with her handbag, and walked away calmly.
   The two astonished youths were sitting on the ground when Mrs. Turner crossed the street towards a door with a lighted sign above it. Mrs. Turner paused, turned round, smiled at the youths and walked into the South West London Judo Club.