Complex sentence: The Queen is also plotting to murder both Imogen and Cymbeline, procuring what she believes to be deadly poison from the court doctor, Cornelius, who, suspicious, switches the "poison" with a harmless sleeping potion.
Split into simpler sentences: The Queen is also plotting to murder both Imogen and Cymbeline. She obtains what she believes to be deadly poison from the court doctor, Cornelius, who, suspicious, switches the "poison" with a harmless sleeping potion.