I was on a sort of retreat.
The retreat was near the ocean.
I don't know anybody there.
Although, in the dream, I do.
Then the police show up.
They say they've discovered a body, out by the ocean.
They say there's a whole in the back of their skull.
My friends and I, wanting to be detectives, go to look at the body.
We have to sneak in, but we do so successfully.
We put on the protective gear, and gloves, and flip the body over.
Sure enough, the hair is shaved away where the hole is.
Looking close, we realize somebody's pushed their finger through the back of the skull.
It's clearly not a bullet hole.
Then I get the feeling that it's somebody on our retreat.
The three of us vow to watch each others backs, and to not be alone in a room with anyone else.
Sitting in the dining hall, we realize there's somebody behind us in the closet.
We get up, and run off.
We lock ourselves in a room (with pool toys), and try to devise a plan.

Then the dream skips ahead, and another body has been found.
Same condition as the last.

Then the dream skips ahead again (and this is the part I remember the most).
I'm in a deserted area.
It's a desolate little place, and the most frightening place I've ever been.
I'm face to face with the killer.
And yes, he's been pushing his thumb through people's skulls.
Now it's my turn, because I figured out who it was.
It was the doctor that came along on the journey.
He stares at me maliciously.
He's holding on to me, and getting ready to "finish the job".
Then I wake up.

The ocean often represents emotions and the unconscious, so a body discovered by the ocean can represent repressed thoughts or feelings that you have tried to get rid of (kill).

A retreat is a safe place, a place you go to in order to get away from bad feelings and ideas.

Police are authority figures who make sure you do what is right, regardless of whether or not it feels good. In the dream, they are making you face up to the thing that you are avoiding.

A finger can be about "pointing the finger at someone" - saying that they are guilty.

In the closet - "skeleton in your closet" - something that you feel guilty about but wish to hide.

The doctor is the killer. The doctor is supposed to help you, but he is hurting you. This can mean that the solution that you decided on in order to deal with a problem (pretending that it never happened?) is actually making it worse.