Complex sentence: Count de Rochefort helps Beaufort escape from his prison, and is subsequently arrested by Mazarin, who then sends d'Artagnan and Porthos after Beaufort, but Beaufort escapes them due to interference from Athos and Aramis, who are working for Beaufort.
Split into simpler sentences: Count de Rochefort helps Beaufort escape from his prison, and is subsequently arrested by Mazarin. Mazarin sends d'Artagnan and Porthos after Beaufort, but Beaufort escapes them due to interference from Athos and Aramis, who are working for Beaufort.