To get the fabled Black Spindle, here's what you do. First, wait until Lost to Light is the daily heroic story. Play through the mission as normal, until you get to the section where you are near the door that goes to the Ketch for the Shadow Thief strike. Enter this door, and proceed to board the Ketch. You will then get contacted by Variks. After this, a ten minute timer will appear. You must clear the Ketch of all Taken enemies before the timer depletes. If you can do this, then the Black Spindle should drop. It is highly recommended to have a full Fireteam of 3. Hope that helps.