A committed, immersive performance by young newcomer Kíla Lord Cassidy spearheads this period mystery set in rural Ireland in the 19th century, where an 11-year-old girl in a highly religious family has been fasting for four months - seemingly without any physical repercussions. Florence Pugh is the young nurse sent to observe the girl - and solve the puzzle for us, of course. Although Pugh's performance comes off as anachronistic at times and the film drags in an uneventful middle section which seems to have little other purpose than to fill out the running time, the mystery itself is clever and incorporates enough historical, religious and sociocultural aspects to make this weighty and effective. And whenever you start doubting the story's potential for veracity, Cassidy's authentic performance sucks you back into this bygone world of repressed guilt, shame and emotions.