When he was finally forgiven and allowed to come out of his cupboard the summer holidays had already begun.
Dudley had already broken the camera he'd just been bought, crashed the radio controlled plane, and on top of all that, on the day he rode his racing bike for the first time he crashed into Mrs Fig, who was crossing Privet road on crutches, and the incident in which she got knocked down had ended.
I can't understand how 終わる is being used in this sentence. My translation of the final clause makes no sense. I'm not even sure if 事件 is the subject or object of the verb.