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