'When Calls the Heart': Nathan Has a Tense Confrontation With Lucas and Elizabeth (Exclusive)

In ET's exclusive clip, Nathan and Elizabeth have a tense conversation following Allie's adoption ceremony. Just as quickly as tension arises, Nathan has to leave town to handle a situation where a prisoner has escaped. Lucas attempts to speak with Nathan as he and his horse gallop out of town, to which Nathan replies, 'Save it.' 'When Calls the Heart' airs Sundays at 9 p.m. ET/PT on Hallmark Channel.