The Jewel of Seven Stars is a locked-room mystery, which is a mystery genre which requires a little extra work in D&D. It’s not enough that all the doors and windows be locked from the inside. At the very least, the room must be warded against teleportation, entry via other planes, and insubstantial creatures passing through walls. Alarm should also be used, to ward against invisible assassins. Without any of these countermeasures, the question becomes not “how could this happen?” but “which well-known trick was used?”
Given these minimum requirements, the only interesting locked-room murder victim is a paranoid high-level spellcaster (or someone – possibly royalty – who can hire one).
The Jewel of Seven Stars is much less well known than Dracula, but it is still a magical fantasy, so the same rules apply. The victim is basically a paranoid high-level spellcaster (steeped in the arcane mysteries of Egyptian mummies). He’s set up his own defensive magic, but he’s been stabbed anyway – in a way that cannot be self-inflicted.
Off the top of my head, here are some fantasy locked-room mystery solutions:
- The victim is the recipient of a voodoo-doll-style curse where they can be hurt remotely.
- One of the trinkets in the room is a hostile Figurine of Wondrous Power.
- Stabbed or bludgeoned by an animate piece of furniture.
- The murderer was admitted by the unsuspecting victim. After the crime, the murderer re-locked the door and re-set the wards, shrunk to the size of a flea, and is STILL IN THE ROOM oh my god Sarah is in there now
- The murderer is a snowman, who melted. (ALWAYS be suspicious of an unexplained puddle of water. ICE IS ALWAYS INVOLVED)