Individual, make ahead beef Wellingtons is the first thing that came to mind.

Prep ahead but not cooked and reheated though.

You didn't say how many courses of the main meal. But in an elegant "haunted mansion", there would be more than just a salad, entree and dessert. And will you have "servants" to serve the meal or would it be buffet? If it's served this is the meal I would do: appetizers in the parlor. Once seated a nice cream soup either homemade or you can buy good boxed soup at Trader Joe's (carrot or butternut squash) and add real cream when you warm it up before serving, a nice salad of spring greens with bleu cheese crumbles dressed with a vinaigrette and served dressed (no passing of dressing), Sarah's chicken (boneless skinless chicken breasts baked in a dried beef lined pan, topped with a half slice of bacon and covered with a sauce of a mix of sour cream and mushroom soup and baked in a 300 degree oven for 2 hours) served with rice and a green vegetable (you know your crowd -- green beans are always good but you can up the ante with asparagus which I would roast) and then I would do Ina's chocolate ganache cake for dessert (because it would go well with hot chocolate). If you want a bit more elegant meal, you could add a fish course (a crab cake would be nice) after the salad and between fish and entree do a small soup of sorbet. If you don't like the chicken dish, I would do pork loin with a sauce and a potato dish instead of the rice. For about six years, my husband and I did wine dinners at a Victorian Mansion here in our little town. We would add a tart and then end the meal with port, fruit and cheeses. Hope this helps.

Great idea. I've never made Beef Wellington before but will go research--thanks much!

When I was growing up in the midwest in a family with 6 kids, my mom often made a casserole with "mystery meat". I know this isn't helpful.

lol seagrass_gw. Helpful in that it made me laugh. :-)

I don't know the time frame of the "story"....but something en papilotte would be do ahead and elegant. A year ago I did chicken tenders,with some diagonal carrot slices, a piece of green onion about 5 inches long and 4 or 5 snow pea pods. I put a spoonful of a "sauce" made from soy sauce, apricot preserves and a fair amount of finely chopped fresh ginger...and put a couple of spoonsful of that in each packet.
Make the packets ahead and refrigerate, and them bake for 20 minutes at 420 and serve. I had rissoto and a salad with spinach and strawberries and a sweetish vinaigrette with white balsamic.

If the mystery dinner is like those I have attended, the cocktail hour is where characters are defined and perhaps when a murder is discovered, so foods that allow for moving around and getting acquainted is good, and through out the evening there are pauses when you can serve dinner or dessert adn when new clues are revealed.
Sounds like fun!

For pudding, Nun's legs springs to mind. We had it at school. It's a jam roly poly but looks like a pale leg with blood inside!

Goulash for the main?

I wanted to follow-up after the party and thank everyone who provided suggestions. The party was a huge hit and all reports are that the food was amazing! After a few weeks of testing options for an entirely pre-made meal here is what we ended up with on the menu:

For cocktail hour in the parlor we had shrimp & cocktail sauce, a cheese tray with crackers, warm artichoke dip with sourdough baguette slices, a veggie tray and bruschetta with tomatoes, garlic, basil and parmesan.

For dinner we had: salad of mixed greens with red onion, candied pecans, dried cranberries and feta. Entree choices were Chicken Marsala, individual Beef Wellington served with a port mushroom sauce, or Salmon served with a lemon, caper and white wine sauce. All entrees were served with garlic mashed potatoes and roast baby asparagus. For dessert we had a 4-layer chocolate torte or a northwest berry crumble with vanilla ice cream.

I rarely post, but I visit this forum often and I just want to say thank you again to you regular posters and advice givers . . .it's always much appreciated! My intention was to take pictures along the way but I was so involved in the party that I only got pic of the salad. Thank you!

Soo....who was the murderer?
Sounds like a lovely evening!!

It really was a great evening! The nanny did it. She killed off the head of the forensic crime lab. Thanks again for the pre-party ideas!

That's a great menu, so glad it turned out so well!

man, i was thinking pickled … beets