Complex sentence: The final acts already booked when the building was destroyed performed the next summer of 1969 on the patio and inside the other Douglas owned establishment, the Golden Horseshoe Supper Club.
Split into simpler sentences: The final acts were already booked when the building was destroyed. So during the summer of 1969, they performed on the patio and inside the other Douglas owned nearby establishment, the Golden Horseshoe Supper Club.