And is there any information as for the secrets that give score points, so that it is Amateur/Advanced/Master Detective obtained for each chapter? I had only 4 'secrets' for the Chapter 3...
Ditto. I completed Chapter 3 without using any hints, and I only got the Amateur achievement, which is annoying.
My guess is you can learn secrets while researching the 4-animal combination on the ship, and you have to ask things / talk to people in the right order.