Prentiss learns that her old friend, Matthew Benton, who recently returned from a trip to Spain, has died of a heart attack. She is clearly very shaken up and her pain is visible for all to see. When she learns of another, similar death, she talks to Hotch and tells him that they may be dealing with a serial killer rather than young men just dropping dead naturally. Seeing her distress, Hotch agrees to help and look further into the cases.
Seems that the dead men DO have something in common. Not just Matthew, but others have recently returned from a trip to Spain where a priest died. Speaking of priests, as we see the BAU noting strange scratch marks on the bedroom floor at Matthew's home, (where Emily is decidedly unwelcome) we see an elderly one performing what is obviously an exorcism and the 'possessed' person is quite obviously mot having a fun time of it at all.
Apart from learning that Prentiss fell pregnant at the age of 15 and that her friend, Matthew, helped her procure an abortion, this episode in itself was extremely predictable and very dull. It WAS good to some a Prentiss-centred piece though.