Complex sentence: Terry attempts to get inside from upstairs, but is thwarted by an umbrella-wielding Nicole... who then signals Larry O'Brien, the Walkers' private security guard, by flashing "SOS" with the light in her room.
Split into simpler sentences: Terry attempts to get inside from upstairs, but is thwarted by an umbrella-wielding Nicole. She then signals Larry O'Brien, the Walkers' private security guard, by flashing "SOS" with the light in her room.