Marpleisextremelyproudwhensheisappointedtotheboardoftrusteesofamerchantmarinetrainingvesselwhosemissionistorehabilitateyoungcriminals.Asinallofherendeavors,MissMarpleintendstotakeanactiveroleinthejobandevenshowsuptotheboardmeetingdressedinnavalblues.Whenafellowtrusteeispoisonedjustpriortohismakingsomekindofrevelation,MissMarpledecidestouseherpositiontospendtimeontheship.Thisupsetsthevessel'sfragilesocialnetworkasshedispossessesblusteringCaptainRhumstonefromhisquarters.Whentwoship'sofficersarelaterfoundmurderedalso,MissMarpleenlistshelpfromherfriendJimStringerandInspectorCraddocktoexposethemurderer.