After dropping down the hole, an elevator will carry the party to the aerie of Venus Lighthouse. Here you'll overhear Saturos and Menardi arguing with Felix and Sheba. Eventually you'll enter battle with Saturos and Menardi.
Defeat them and another cutscene will follow. The Venus beacon is lit, Felix and Sheba leave, and Saturos and Menardi merge to form the Fusion Dragon, attacking the party.
Once the dragon is defeated, another cutscene leaves Isaac and friends back in Lalivero. They resolve to seek out Jenna and find Lemuria, and receive the Black Orb needed to pilot Babi's ship. Enter the guarded building in the northwest corner of Lalivero town and walk to the end of the gangway. Use the Black Orb to access the Lemurian Ship.