Complex sentence: His own schemes having failed, he began plotting to murder the aged Andronikos II and seize the throne for himself, but the plot was foiled, and Syrgiannes was sentenced to life imprisonment.
Split into simpler sentences: His own schemes having failed, he began plotting to murder the aged Andronikos II and seize the throne for himself. The plot was foiled however, and Syrgiannes was sentenced to life imprisonment.