Gianna Mackey joins Firehouse 51 as its newest paramedic. 

Cruz, who grew up with Mackey, is very protective of her and does his best to deter Gallo from any sort of romantic inclinations.

Mackey isn't phased, and upon learning this, makes a loud comment about her and Gallo going out within earshot of Cruz.

Mackey and Brett respond to call where a man has overdosed.

They go to help him but the man's brother pulls a gun on them.

They make it out all right, but later learn the man has died.

When Brett gets back to her apartment, she sees that the door is unlocked.

She calls Casey and he spends the night on the couch.

Kidd tries to get Girls on Fire restarted and is successful. She also finds a creative solution to rescue Severide when he is trapped inside a photography studio during a fire.

These actions lead Boden to suggest Kidd take the upcoming lieutenant's exam.

While she has hesitations, Severide encourages her.

Herrmann, Mouch, and Ritter come up with a plan to advertise the opening of Molly's Patio and set out to create a 'treasure map' of sorts to drum up business.

At the end of the episode, Ambulance 61 is dispatched for a call but are being followed by the gunman. They crash and both the ambulance and his car go over the edge of a bridge.