I have many favorites but i think it have to be either when Will accidentally got an overdose by a patient ( 8x7 ) or when they have the toxic chemical spill in the hospital and Ethan got really bad and Will was hurt also. Both Connor and Ava had also to they in the hospital to help a patient to survive. ( Season 4 , maybe more then one part but it is starting on episode 7 and then maybe forward ).
