“NCIS” Season 13 returns on Jan. 5 with an explosive two-part crossover special with “NCIS New Orleans.” The episode, titled “Sister City,” will feature both the Washington D.C. and the New Orleans NCIS teams delving into a very personal case which involves Abby Sciuto’s (Pauley Perrette) brother, Luca (Tyler Ritter). [Spoiler Alert!]

Cartermatt shared the synopses for episode 12 of both “NCIS” and “NCIS New Orleans.” Here’s a summary of what will take place:

The passengers and crew of a private aircraft flying from New Orleans to Washington D.C. will be lethally poisoned, and the main suspect will be the chef who prepared the meals for the aircraft. He will unfortunately turn out to be Luca, Abby’s brother. The NCIS team will investigate the incident, and they will be working in close coordination with the team in New Orleans, where the flight originated from.

Special Agents Jethro Gibbs (Mark Harmon) and Dwayne Pride (Scott Bacula) will get their teams together on a mission to find Luca and to solve the murder mystery. The passengers on the flight are from a private tech company, and the NCIS teams will try to find out why they were targeted.

Meanwhile, a Russian sleeper agent who has had some involvement with Luca will also be investigated by the NCIS New Orleans team. Sebastian (Rob Kerkovich) will fly to D.C. to work with Abby, While Bishop (Emily Wickersham) will head to New Orleans to work with the team there.

“Sister City,” the “NCIS’ Season 13 and “NCIS New Orleans’ Season 2 crossover, will air on Jan 5. Part 1 will be at 8 pm and Part 2 will be at 9 pm ET on CBS.