My London grandparents

My grandfather told me the story of how they met. He was on sentry duty, in his sentry box outside West Ruislip Raf station when some local lads he knew, and didn´t much care for, came by with their sister in tow. They amused themselves for a while by mocking him and insulting him, while he stood compulsorily immobile in his box, then they moved on. He was then amusing himself thinking of evenge he could exact, when the girl came back without her brothers. And here I am to prove it.