"Criminal Minds" recently kicked off with its season 11 premiere episode last Sept. 30. The group of brilliant crime-fighting agents are now back and the last episode was packed with so much action since the team was seen taking down the unsub, who painted his victims' faces.

The premiere episode also saw the entry of Aisha Tyler, who plays forensic psychologist Dr. Tara Lewis. Tyler's character assisted the Behavioral Analysis Unit (BAU) in pursuing episode 1's usub.

On tonight's episode, it's another case for the unit and according to Spoilers Guide, the episode titled "The Witness" will give the team a case of a gas attack.

For the second episode, the team will be heading to Los Angeles, where somebody attacked a bus using sarin gas.

Based on the promo clip (via Design&Trend) for the next episode, it can be seen that Garcia (Kirsten Vangsness) informs the team that there were 10 people who died from the said gas attack.

Hotch (Thomas Gibson), Derek (Shemar Moore), and Reid (Matthew Gray Gubler) are spotted at the crime scene piecing the clues together so they'll be able to catch the perpetrator.

It is revealed that the device behind the attack was time-controlled, as Reid states, adding that once the gas is released, it has the ability to kill several people in just a matter of minutes.

It's up to the BAU to do their jobs quickly to avoid bigger attack in Los Angeles.

For the second episode, two new faces can be seen. Tim Kang, "The Mentalist's" Kimball Cho, will guest star as a medical supply worker and "NCIS'" Marisol Nichols will also join in.

Nichols will play Natalie Colfax, an FBI-agent based in Los Angeles, who will help the team catch the criminal.

Meanwhile, fans of J.J. (A.J. Cook) should wait for several more episodes before they get to see the well loved BAU member.

It was revealed in TV Guide that Tyler will only be staying in the show for six episodes and Cook will return by the seventh episode.

Catch "Criminal Minds" season 11 episode 2 when it airs tonight, at 9 p.m. EST on CBS.