Well I know of two TRUSTWORTHY sources that have watched the episode already and spoiled a little.

SPOILER ALERT

1. Someone from the past "long gone" comes back.

2. There are MULTIPLE CASUALTIES from the bomb. Goodbye Stiles and Haffner. We know Smith and Bertrum live so I assume it's the visualize duo since they're together when the bomb goes off.

3. Something in the last minute CHANGES THINGS FOR THE CBI moving forward.

4. Something from season 2 is explained.

Obviously I have believed that BP is red john from the beginning, and this is a spoiler.

Patrick strangles RJ in a park and watches him die. TV guide has already reported that. Now I ask. Do you think he could strangle Bertrum or Smith? F no. Now a skinny guy like BP?!?!?!?!?!