WHAT DO I NEED ALL THE SHARDS FOR?

You need to collect all the shards before you can use them.

We assume you've unlocked the desk drawer in the room that was guarded by Kitten.

Has Pixie brought you a set of shards?

And have you taken the remaining shard from the safe?

If not, come back when you have.

You now have all the shards. Tap the half-finished mosaic for a closeup and use the shards on it.

You now need to rearrange them in a way that makes sense.

Arrange the shards so that all adjacent sides have matching symbols.

There's one more thing to do.

Do you see the tiny hooks on the sides of the mosaic?

What could they be for?

They are around the height of the neckline, more or less.

Some sort of necklace, maybe?

Use the amulet you found in Busby's pocket on the hooks.