That's why it came with a player's guidePatcheresu wrote:
3. I have discovered a HUGE bug that if done properly, let's you skip the 5th and 6th dungeons and not even know that there was a key item in the sewers. What kind of jerk listens in on phone calls made for museum curators anyway? If you just avoid the phone conversation that ties in to Venus, the Plague-Infested Rat, and the signature then the game won't tell you what you did wrong unless Hint Man would offer his services.

And I agree with the other statements, sort of.