Go through the Forest once to open the road to the River
Go through the River to open the road to the Cave.
Enter the cave and fight the scripted fight against a commander. Polon will take you to her home in Rococo and realise that you are a doppelganger of Rask.
There you'll meet Count Prinky and Igor. They are stare at a solid piece of air. This is a hint to put on your Glasses to be able to see the cloaked spaceship.
Make your way to Part 2 of the Cave, occasionally using your Drill to open passages, until you meet a commander (3) with a passage that cannot be drilled.
Use Vanish or Change and wait for him to open the secret door.
On Part 3 you will trigger the trap and fall to Part 4 (1).
(Note that Vanish will be disabled for the trap to work.)
Because of the fall you lose Drill and Light. And you're back-attacked.