Relationships are challenged at Station 19 following Sullivan’s actions at Maya and Carina’s wedding, putting his marriage with Andy to the test. Dean comes to terms with his feelings for Vic, while Travis rekindles an old flame. The annual Phoenix Festival brings out some reckless behavior in some of Seattle’s citizens, challenging the teams at Station 19 and Grey Sloan Memorial. The crossover continues on Grey's Anatomy S18E01 Here Comes the Sun (II).

Andy and Sullivan’s relationship continues to be tested. Meanwhile, Emmett joins Dean and Vic on a mental health call, and Maya does some soul searching.

When a heat wave hits Seattle, Station 19 becomes a cooling center and chaos ensues with locals who aren’t used to the extreme temperatures. Andy deals with regret and finds a friend in Theo. Joey comes face-to-face with his past during a ride-along with Ben and Jack

Diane returns to help with Crisis One intervention training for Station 19 and Station 23 firefighters. Meanwhile, Andy and Sullivan continue to be at odds, and Jack helps a young autistic man on a city bus.

When Theo and Vic hit a relationship milestone, Vic is forced to reckon with her feelings about commitment. Andy takes refuge at Dean’s home and helps care for Pruitt, while Dean considers a new potential career opportunity. Meanwhile, an explosion rips apart a neighborhood and changes the lives of our firefighters forever.

Station 19 and Station 23 each attempt to celebrate Thanksgiving following the fallout from the neighborhood explosion. The firefighters come together to cook, toast to loved ones they have lost, and celebrate the families they have become.

Vic and Jack lean on one another as they process the loss of Dean while Ben and Bailey try to convince Dean’s parents to allow them to raise Pru. Meanwhile at Station 23, Andy’s role temporarily expands and Sullivan subs in. Carina and Maya explore growing their family

It’s the most wonderful time of the year and the firefighters have their hands full responding to a number of crises throughout Seattle. Putting aside their differences and personal drama, they come together to try and achieve a Christmas miracle.