The Convent San Tanco suffers through a heat wave. Then Sister Bertrille arrives with air conditioners, wangled from Carlos Ramirez, when he installed new ones in his casino. Meanwhile, gangster Rufus Morgan on his yacht, tells his men, Remick and Martin, that they're taking over Carlos' operations. Pedro, coming to warn Carlos, finds him with lovely Doris Finch. Carlos is worried but determined not to give in. Sister Bertrille's arrival suggests a way out. When Morgan's men come, Carlos introduces Sister Bertrille of the Convent San Tanco as new owner of the casino. Sister Bertrille explains to the disapproving Mother Superior it's just for a few days until Morgan leaves. Carlos hides out on his yacht. Mother Superior at first refuses, but stands up to Morgan's men, even threatening to call the police. Remick and Martin report to Morgan. He summons Sister Bertrille to the casino and insists she play poker with him. With no limit, Sister Bertrille loses steadily. Morgan is sure he's won until Sister Bertrille, bluffing in the final decisive hand, saves the casino. Pedro is sure Carlos is still in danger. Sister Bertrille flies out to Morgan's yacht. Morgan, very superstitious, feels Lady Lucky is flying outside. Heeding her plea to be easy on Carlos, Morgan leaves. Mother Superior rebukes Sister Bertrille. However, she takes full responsibility and asks Sister Bertrille to explain her poker strategy to the Monsignor.