Girl Wonder and the Terrific Twins Book

Katie's stepfather has just died, and she, her mother, and step-brother move to a fictional small town that I gather is in the Upper Peninsula of Michigan. They will be living with and taking care of Uncle Frank, who is actually no relation to them. Newquay is a former mining town that is currently almost dead. The mine had collapsed 30 years prior, killing several men and giving rise to tales of 'knackers,' the ghosts of miners, turned evil and trying to tunnel their way out. Katie does see a ghost, but it's not a miner and doesn't seem evil, either. Actually the ghost is quite helpful. Other issues explored in the book include Katie's stepbrother Jay not feeling welcome in a family that no longer includes his dad, and so becoming a trouble-maker in an effort to get sent away.
A fun, quick read. Interesting incorporation of local lore and Cornish customs. Ages 9-12.