Things are heating up in "Chicago Fire" season four. The situation has become so much worse for Chief Boden and his family, especially now that Serena is missing. With Boden fighting to clear his name and Firehouse facing more time under Captain Patterson, Severide works to find Boden's missing accuser.

In "When Tortoises Fly," the eighth episode of "Chicago Fire's" latest season, Boden's (Eamonn Walker) accuser goes missing after his wife Donna (Melissa Ponzio) confronts her in public. 51's chief realizes that Maddox might be the one who set him up after he's paid a visit by the State Attorney. Boden is later arrested while relaxing with his crew at Molly's.

With Boden temporarily out of the picture, someone has to step in. A synopsis laid out in the "Carter Matt" site describes the Firehouse 51 crew unhappy that Captain Patterson (Brian White) is sitting in for Boden. Severide (Taylor Kinney) is going all out in his quest to help Boden and finds out where Serena (Ilfenesh Hadera) might be hiding. This information prompt's "Chicago P.D's" Officer Atwater (LaRoyce Hawkins) and Officer Ruzek (Patrick John Flueger) to go to Lake Carlyle to look for more evidence on Boden's case. The other members are also faced with their own problems as friction rises between Jimmy (Steven R. McQueen) and Chili (Dora Madison). Herrmann (David Eigenberg) and Otis (Yuri Sardarov) find Freddie (Ralph Rodriguez) a job that would keep him near them.

Episode nine feels like a crossover episode with "Chicago P.D" based on the synopsis, but the trailer certainly doesn't give any indication of that. As a matter of fact, a sneak peek of the upcoming episode, "Short and Fat," focuses on the dangers that the firefighters of 51 face daily.

The short clip starts with a scene of an accident and a driver warning responders that the tank he's carrying is enough to knock down the whole neighbourhood. The 51 crew sees a tank that seems to be leaking some kind of chemical and Severide says they can't evacuate everyone in time. Severide, Casey (Jesse Spencer) and the others transfer the smoking tank to their truck and drive away. The scene fades to black and an explosion is heard.

Fans are undoubtedly hoping that these brave men will survive that explosion. Viewers will find out the truth when episode nine of "Chicago Fire" season four airs on Dec.8.