This quest line is given by Commander zavala in the Tower after completing the first Taken King story mission on Mars.
* If the achievement does not unlock do the log out trick
*This is the Titan's Subclass Quest.
* You have to conduct this quest alone
After a linear quest that you have to do you will be given the Sunbreakers' quest which is actually 2 short missions on Venus. After completing both you be instructed to return to the tower and after you turn the quest in the achievement will unlock.