These mysteries keep the investigation grounded while allowing one impossible fact to change the rules: a town forgets a person who existed, or an old bell keeps intruding on a cold case that should belong entirely to the past.
The supernatural element is not decoration. It changes what can count as a clue. In The Hollow Year, absence and failed memory become evidence that someone has been erased. In The Hollow Bell, a decades-old disappearance and a body beneath the ice collide with a local legend that refuses to remain only a story.
Enid knows someone is missing even when nobody else remembers him. A second mug, a phone number, and the shape of an absence become clues in a mystery where memory itself cannot be trusted.
The mechanism: proof of a forgotten person has to survive after the town's living memory does not.
Journalist Claire Renner returns to Millbrook Falls while Sheriff Del Hutchins investigates a discovery that reopens a case the town never escaped. The evidence is physical; the bell is harder to explain.
The mechanism: a grounded cold-case investigation keeps colliding with a local legend that may be more than folklore.
Start with The Hollow Year if you want reality and memory to become the puzzle. Choose The Hollow Bell if you want a sheriff, a journalist, a frozen-body discovery, and an old town legend pressing against a grounded investigation.