Borderlands 3Blood Drive

"Blood Drive" is the 17th Main Story Mission and is unlocked when you complete "Cold as the Grave".

The Calypsos have kidnapped Tannis and are going to execute her for the entertainment of their followers for an Eridium pledge drive! Unless you can stop them, they’ll use that Eridium to charge the Pandora Vault Key! Also, Tannis will die, which is also bad, so maybe you should stop them.