Calus beat us to the Veil and secured it on behalf of the Witness. Luckily, its containment infrastructure should delay their efforts, at least for a little while. Based on Ghost's strange experience, it appears Calus intends to use a device called the Radial Mast to link the Veil with the Traveler.

Whatever the Witness wants, this can't be good. With Calus's forces focused on the Veil containment, Osiris wants us to hit Calus's fortress directly and take out this Radial Mast before it is moved closer to the Veil. Even despite Rohan's concerns.

Nimbus recommends you check in with Rohan and Osiris at the Hall of Heroes before moving on to mission "Downfall."