For countless centuries, the Tenno have been dormant, but with the Grineer Empire on the rise, the Lotus begins tracking down and awakening the Tenno. Unfortunately for the Lotus, Captain Vor has been one step ahead of her so far and has been killing off the Tenno as they awaken, before they are strong enough to stop him. His latest find takes him to Earth, near an Ostron village, where he finds a dormant Tenno just as the Lotus reawakens them.
This time, however, he has a different plan—to capture said Tenno. He attaches an Ascaris device to the Warframe, ordering his soldiers to spare it; he intends to use the Ascaris to control the Tenno, and take it to the Twin Queens as his prize. Presumably the first of many or a proof of concept, Vor would then seek to capture more Tenno; once armed with loyal Tenno soldiers, the Grineer Empire would become unstoppable.
The player must evade Vor and his soldiers, arm themselves, restore a ship to functioning order with the help of ship Cephalon Ordis, and ultimately confront Vor to put a stop to his plans.