The listing, The Boxcar Children: The Disappearing Friend Mystery has ended.
Henry, Jessie, Violet, and Benny used to live alone in a boxcar, but now they live with their grandfather. And they've just made a new friend named Beth.
The Boxcar Children decide to raise money to help the Greenfield hospital. At Beth's suggestion, they form a service called the Boxcar Helpers- to babysit, wash cars, mow lawns, and care for pets. But Beth keeps disappearing. And then other things start to go wrong. Is someone trying to put them out of business?
Book 30 of the Boxcar Children Mysteries. (Not in perfect condition; published in 1992)