Complex sentence: Fletch paniced when he saw Josh coming up the stairs and tried to bundle him back in, but Fletch overpowered him and accidently caught Hannah in the face and knocked her down, and then escaped from the Ashworths'.
Split into simpler sentences: Fletch paniced when he saw Josh coming up the stairs. Josh tried to bundle him back in, but Fletch overpowered him and accidently caught Hannah in the face and knocked her down, and then escaped from the Ashworths'.