It's been said a full moon increases the chances of something odd taking place. This can be an increased number of patients in an emergency room or perhaps books flying off the shelves in a municipal library. Literally. Police can often see an increase in how many folks are hauled in on public drunkenness charges. Therefore, Det. Kate Beckett (Stana Katic) is not too surprised when she has to work on Halloween. Good thing Richard Castle (Nathan Fillion) can lend a hand.
The corpse is not the issue. However, one which reposes in a cemetery with a stake nearby bears closer scrutiny. Lanie (Tamala Jones) believes this is not what killed the young man. Rather, blunt force trauma did. In layman's terms, blunt force trauma is a non-penetrating injury to the body due to accidental injury or deliberate attack (as opposed to a penetrating injury like a knife or gunshot wound). Head trauma can easily be fatal with one blow, especially if it causes brain injury.
Castle thinks the gravestone within close proximity might also be a clue. He's right, as it links back to the disappearance of a woman close to 20 years ago. A graphic novel is perhaps the biggest lead of all, with illustrations of great detail.
While the plot is too convoluted to attempt to explain here, the killer is even more of a doozy. Secrets come in all shapes and forms, but they always hide in the dark. Exposed to light, any power gets vanquished.
Since this episode airs the week of Halloween, of course costumes must come into play. What Castle starts out with is especially sweet. I'd hate to ruin the surprise, so you'll just have to watch. Keep in mind Fillion has made his living on several projects, including a series or two. True fans should not have any problem recognizing the symbolism. For other characters, the revealing comes at Castle's party. Jon Huertas is in camouflage, which makes sense. The actor has a military background. Seamus Dever takes on a doctor, and Tamala Jones shows savvy as a blue-sequined cat.