ThestoryconcernstheWaterburyfamilywhomoveto"ThreeChimneys",ahouseneartherailwayafterthefather,whoworksattheForeignoffice,isimprisonedasaresultofbeingfalselyaccusedofsellingstatesecretstotheRussians.Thethreechildren,Roberta(Bobbie),PeterandPhyllis,findamusementinwatchingthetrainsonthenearbyrailwaylineandwavingtothepassengers.TheybecomefriendlywithAlbertPerks,thestationporter,andwiththeOldGentlemanwhoregularlytakesthe9:15downtrain.Heiseventuallyabletohelpprovetheirfather'sinnocence,andthefamilyisreunited.ThefamilyalsotakecareoftheRussianexile,MrSzczepansky,whocametoEnglandlookingforhisfamily(laterlocated)andJim,thegrandsonoftheOldGentleman,whosuffersabrokenleginatunnel.
