FatherBrowntriestotransportahistoricallyimportantcrosstoRomeengaginginbattlesofwitsandfaithwithathiefandpursuingpoliceman.Thethief,namedFlambeau(Finch),isamasterofdisguiseandiselusive,asFatherBrownpursueshimandtriestoconvincehimtoabandonhiscriminalcareereee
Duringthemakingofthefilm,AlecGuinnesswasmistakenbyasmallboyforanactualpriest.ThisepisodeappearstohaveplayedapartinGuinness'slaterconversiontoRomanCatholicism.