| I A MYSTERIOUS HOUSE | 1 | (12) | |
| II THE OLD-FASHIONED KEY | 13 | (10) | |
| III THE SEARCH BEGINS | 23 | (10) | |
| IV THE SECRET TRAP DOOR | 33 | (10) | |
| V FREDDIE'S ADVENTURE | 43 | (10) | |
| VI THE PROWLER | 53 | (9) | |
| VII A KITE RIDE | 62 | (11) | |
| VIII TWO BOY DETECTIVES | 73 | (10) | |
| IX THE HIDDEN ENTRANCE | 83 | (9) | |
| X CATCHING A GHOST | 92 | (10) | |
| XI A RUINED CAMP TRIP | 102 | (11) | |
| XII A MIXED UP GET-TOGETHER | 113 | (9) | |
| XIII A RUNAWAY PET | 122 | (11) | |
| XIV HOPEFUL HUNTERS | 133 | (10) | |
| XV A NEW CLUE | 143 | (10) | |
| XVI THE TWINS' TRICK | 153 | (8) | |
| XVII A CONFESSION | 161 | (8) | |
| XVIII THE TREASURE | 169 |