"Lair of the Harpy" is the 12th Main Story Mission and is unlocked when you complete "Hammerlocked".
Aurelia Hammerlock, Sir Hammerlock’s sister and CEO of the Jakobs Corporation, is offering to pay you to leave Eden-6. She’s invited you to Jakobs Manor to negotiate. It’s almost certainly a trap. It’s also the only way to find the Eden-6 Vault Key.