Complex sentence: After leaving Lórien, the Ring's evil and corrupting powers begin to show-when Frodo is alone for a while to decide the future course of the Fellowship, Boromir tries to take the Ring from him.
Split into simpler sentences: After leaving Lórien, the Ring's evil and corrupting powers begin to show. When Frodo is alone for a while to decide the future course of the Fellowship, Boromir tries to take the Ring from him.