Summoner's Circle is a story mission in The Taken King. It takes place on the Dreadnaught as the first stage of the Quest The Road to King's Fall which involves eliminating the Infantine Ogre from being infused with Taken power.
The Guardian heads towards The Founts by way of the Mausoleum. Upon entering, a deafening roar rocks the condemned prison. They soon find a group of Acolytes led by a Wizard. The Guardian kills them and finds a polyp from the Wizard's corpse. After finding two more Wizards with polyps, Eris speaks:
The Guardian finds a tomb husk floating above a shrine.
The Guardian picks it up in their hands. However, another roar is heard, much closer.
Several Ogres appear. Preoccupied with holding the tomb husk, the Guardian runs past them. They eventually find shelter deeper within The Founts. The Guardian finds the black liquid pool, guarded by Knights and Acolytes. They put the Tomb Husk inside. A rumbling is heard, and the Guardian steps back. A large Hive Ogre slowly crawls out of the black pit, accompanied by several Thrall and Cursed Thrall. As The Infantine emerges, it slams its fists on the ground in rage.
The Guardian is attacked by the Infantine, Cursed Thrall, Knights, and Ogres. However, the Guardian triumphs, and The Infantine falls dead to the ground.