Clock ticked.

 New book scan for you, this one is While The Clock ticked and it's one of those with both an original and a revised text.

Original

The boys are given a case by the banker Mr. Dalrymple. Apparently someone has been sending threatening messages into, what is essentially a panic room, he's been using as an office. The notes appear when the time lock is on and appear in the middle of the room with no other means of entry. The ex Purdy mansion, has been derelict for a while before he decided to buy up the place. 

There is a subplot of harbour thieves using the mansion as a base to store loot and furthermore strange screams can be heard at night, warning people away. Finally Hurd Applegate reappears from his introduction in The Tower Treasure, as somebody as stolen his precious stamp collection.

Remake

The boat thieves plotline is much more outlined in the remake, with the Sleuth being taken and used to ferry goods without the boys knowledge, and the docks playing much more of a role than in the original. Hurd Applegate has his Jade taken rather than his stamps in this version, and their chums are fully in on the deal instead of being peripheral characters.

Conclusion.

The original is the better story here, but not by much. A few things that I thought would have been in the original are not, such as the dock scenes for one. Also this is the part in the UK versions where the Sleuth is introduced as is Hurd Applegate. Both their official unveilings are in much later books, The Shore Road Mystery 17 and The Tower Treasure 31 respectively. Both are worth your time.

Anyway original here remake here.