HOW DO I GET PAST THE FIERCE GUARD DOG?

Short answer, you can't. Not just yet, anyway.

Longer answer, there may be help nearby.

Turn around to find Calvin.

Make sure to talk to him about your dagger.

Look at the wall when he steps away from it.

What could you stick in these slots?

Your dagger fits in very nicely. Where to place it, though?

You have a hint on you.

Look at the invitation.

Those I's look almost like daggers.

There were two rows of 6 slots each on the wall.

BODKIN is a 6-letter word. So is AWAITS.

Stick your dagger to a slot corresponding to one of the I's on the invitation.

You'll need one more dagger.

Calvin has one.

Talk to Calvin again.

Go to the slots again and tap the slot corresponding to the other I.

The correct positions are 5th slot on the top row, 4th slot on the bottom row.

Turn around and leave via the secret exit that just opened.