What happened at midnight /
by Franklin W. Dixon.
- New York : Grosset & Dunlap, c1995.
- 173 p. : ill ; 20 cm.
- Hardy boys mystery stories ; 10 .
- Dixon, Franklin W. Hardy boys mystery stories ; 10. .
Frank and Joe Hardy become involved in a large and dangerous conspiracy while trying to keep the valuable invention created by one of their father's clients from falling into the hands of thieves.