The Secret of the Old Clock The Hidden Staircase
| Publisher | Grosset & Dunlap |
| Series | Nancy Drew Mystery Stories |
| Other | Twin Thriller Edition |
| Format | Hardback |
| Language | English |
| Location | New York |
| Copyright | 1977 |
| Other | 10601 |
| Notes | Purple Cover, Twin Title |
Added by jlkrien