A gang of five diverse oddball criminal types rent a two room apartment in an isolated house on a London cul-de-sac from an octogenarian widow with three pet parrots. The group's mastermind, Professor Marcus, tells her a cover story that they are members of an amateur string quintet and would like to use the rooms to hone their musical skills.

In reality, they are plotting to rob a bank and plan to use Mrs. Wilberforce's naiveté and her Victorian sensibilities to their advantage.