Hi Mavisf, you'll need to give us more info on what exactly you have done in order for us to steer you in the right direction. Listing locations and evidence you have managed to pick up is helpful, otherwise Poseidon has nothing much to go on other than encouraging you to think carefully.
I will be setting up an evidence only list [less detailed than the walkthrough article] at the top of this forum that might be helpful.
Also, the red herring does not have a active hotspot that lights up your cursor, but you can collect it by clicking on it.