Kelly, Matt, Jay, Adam, Will and Connor have known each other since childhood and have been best friends ever since. Together with Stella Kidd, Sylvie Brett, Kim Burgess and Natalie Manning they live in a large 12-room house.
Finley is Kelly's 10-year-old half-brother and is in 3rd grade at the International Sport School in Chicago. He lives with his parent's and 5 siblings, but they don't really care about him.
Kelly picks him up whenever possible to be there for him and spend time with him. He enjoys playing football and ice hockey and enjoys skateboarding.
Chloe Casey is the 26 year old sister of Matt Casey. Both siblings working for firehouse 51 as well as Matt being Chloe's lieutenant of truck 81, a lot has already happened in their lives. Chloe is best friends with Otis ever since he joined the fire house 6 months into Chloe's candidacy making himself the new candidate. Things have changes at 51 since the death of Andy Darden, there's a new candidate, tensions are high between the lieutenants of truck 81 and squad 3, and sparks are flying between Chloe and Otis.