In which Holmes and I retreat to a secluded Cornish cottage for restorative quietude, only to be summoned into a perplexing and tragic mystery involving a family stricken by a baffling affliction that defies natural explanation. With patient observation and careful experimentation, Holmes pursues the tangled threads of motive and method beneath the eerie gloom cast by an exotic and potent poison, leading us through shadows both earthly and strange.