Collect the materials to make a Crystal of Stealth from Green Bell and Rossica. You will need 5 of each, then report to Horus.

Show Quest Info

Introduction

Horus wants you to help him defeat Set. Since you require Set's Blood anyway, you readily accept his proposition. You will have to confront Set in his temple. However, first you will need to get into the Serra Camp to destroy their totem that conceals the temple. Since the totem is heavily guarded, you should gather materials for a Crystal of Stealth so you can infiltrate the camp.

NPC Dialog

Since you are worthy and we are in agreement
about our plan, I will tell you how we will find Set.
He is in his hidden temple, and to get there you will
need to first infiltrate the Serra Camp. The Serra
Tribe built a mysterious totem to cast an illusion and
protect Set's Temple, making it impossible for me to
locate it from the sky. You should gather materials
to make a Crystal of Stealth to sneak back into
Serra Tribe. You will need some Green Bell and
Rossica.

Quest Completion

Wonderful! Ill make you a Crystal of Stealth.
Remember, its effects will not last forever, you will
have about two minutes to infiltrate their camp.