Complex sentence: Besides trying to get Angel to break his isolation, Doyle also has a personal agenda--he wants Angel to put in a good word with Cordelia for him, without letting her know about his demon heritage.
Split into simpler sentences: Besides trying to get Angel to break his isolation, Doyle has a personal agenda as well. He wants Angel to put in a good word with Cordelia for him, without letting her know about his demon heritage.