The next Main Story Quest can be found on Earth. Just north of the “Mantle” Mission node is a unique-looking zone called Cetus. This is not a Mission node at all. Rather, it’s a special hub safe from enemies where Tenno can gather and meet colorful characters known as the Ostrons.
Once you reach Cetus, you’ll unlock the ability to complete Bounties for a man called Konzu. This will introduce you to your first open landscape in Warframe: a wide-open area called the Plains of Eidolon where Konzu’s Bounties take place. Unlike other Missions in Warframe, extracting from the Plains of Eidolon requires you to exit via the doors to Cetus. Konzu’s initial Bounty will guide you there upon completion, but it’s an important detail to remember!
At the start of the Quest Saya's Vigil, Konzu will begin by asking you to complete one of his Bounties. Do so to prove yourself and continue to the next step of the story!