Complex sentence: After a long battle in a ruined London, Shepard survives being greatly wounded by Harbinger, the most powerful reaper, and arrives at the Citadel beam, where Anderson is being held hostage by the Illusive Man.
Split into simpler sentences: After a long battle in the ruins of London, Shepard arrives at the Citadel beam. A greatly wounded Shepard makes it to the beam and is transported to the Citadel, where Anderson is being held hostage by the Illusive Man.