In which Dr. Arrowsmith confronts the grim reality of a plague-ridden island, navigating the tangled webs of local authority and scientific rigor to pursue a delicate experiment amidst widespread suffering and scepticism. Secured at the estate of the steadfast Cecil Twyford, he encounters his strikingly similar sister Joyce, whose spirited presence stirs both distraction and introspection as the weight of duty presses upon him.