What is the act of contrition in the Catholic Church

Vera warns Framton that her aunt never accepted their deaths and believes that some day the hunting party will return. In anticipation, Mrs. Sappleton leaves the window in the front room open so that they may re-enter the house. When Mrs. Sappleton enters the room and discusses the hunting party, Framton is deeply disturbed by her delusion. However, his concern turns to pure horror when he sees three male figures dressed in hunting gear approaching the house.