Skye has a disturbing dream involving a baby and a music box. Is this a memory? If so, what's the significance of the music box?

During a mission briefing, the entire team is brought up to speed regarding the ancient city. It is located beneath Old San Juan, Puerto Rico. There are white markers representing vertical airshafts which are possible entry points to the city. However, most of them are underwater. Only one will allow a survey team to enter the underground city. If successful, they will locate the temple and blow it up.

Meanwhile, Skye and May's mission is to recover Raina before HYDRA does. Agent Koenig's umbrella cloaking gadget easily does the trick.

Simmons and Bobbie discuss the underwater incident that lead damaged Fitz. Jemma confesses that she's never felt anything but friendship toward Fitz. However, he clearly has stronger feeling for her making things awkward between them.

Skye and Raina sit down to talk. They have an important conversation about Skye's father and the Obelisk. "My grandmother came from a long line of special people who believed in a story about the blue angels that fell from the Heavens. The ancients called them "The Kree" Raina explains. 

At the entranceway to the mysterious tunnels in Old San Juan, Bobbi's contact gets spooked. The locals refuse to go down there as they believe the tunnels to be haunted. Coulson and his team are on their own.

Fitz's remote controlled flying drones come in handy but short out when they descend into a dark cavern. Mack volunteers to be lowered into the cavern and discovers alien symbols on the floor. He makes the unfortunate decision of touching them and soon goes berserk. When he's pulled out of the cavern he attacks the others. Coulson knows this is no longer Mack.

Bobbie take him down and Mack plummets into the dark cavern below. Is he dead?

Our heroes are unaware that Raina has been fitted with a tracking device. This allows Whitehall's Quinjets to locate the cloaked bus.

Ex-Agent Ward boards the bus and convinces Raina and Skye to go with him. Interestingly enough, though Ward's orders were to destroy S.H.I.E.L.D.'s plane, he opted to let the bus go. Is the villain really turning over a new leaf?

HYDRA is now in possession of both the Obelisk and Skye. Will Whitehall unlock the secrets of the ancient temple before Coulson does?