The Ladykillers (1955)

An octogenarian widow (Katie Johnson), living in a tumbledown house near St Pancras Station, takes in a new lodger - a strange ‘professor’ with prominent dentures (Alec Guinness in one of his most vivid disguises.) He has four oddball friends who visit regularly for the purpose, she is told, of playing chamber music. In fact they are criminals, plotting a bank robbery, intending to use the house as their headquarters.