Complex sentence: Ernst befriends Nandl, a fellow patient, and over time becomes cognizant of Dr. Veithausen's plans to execute the patients in the institution, and therefore attempts to work out an escape plan to save Nandl and himself.
Split into simpler sentences: Ernst befriends Nandl, a fellow patient, and over time they become aware of Dr. Veithausen's plans to execute the patients in the institution. He attempts to work out an escape plan to save Nandl and himself.