A couple of nuns in a convent are talking about what they really desire. Sister Angelica claims she has no desire, but the other nuns think they know better: she wants to be with her rich family! When one of that family comes to the convent to ask Angelica to sign away her inheritance, she says that that is one offer too much. She already had to say goodbye to her son, seven years ago.
That son was an illegitimate offspring, taken from her immediately after his birth. The visiting aunt doesn’t want to admit it at first, but then tells Angelica her son died of a fever two years ago. Emotionally destroyed, sister Angelica signs the documents and the aunt leaves.
In the night she is called from paradise by her son. She drinks poison to be with him, but then realises that in doing so she commits a mortal sin and will not be allowed to join him in heaven. She prays to the holy Mother to rescue her from this fate, and she finds redemption: her son runs to her to embrace her.
In short, the story of Suor Angelica, the second of the trio of operas called Il Trittico. Puccini started on these short one acters in 1904, and the premiered in the Metropolitan in New York in 1918. This recording is from 1975. I do not know other recordings of these works, but for me this one is very good. This is Puccini in his prime, dealing in all three operas with a concealed death.