'24: Legacy' season 1 episode 4 spoilers: CTU's HQ is under siege; can Carter-Grimes team up locate terrorist group?

Barely three hours into the season and the Counter Terrorist Unit (CTU) has already lost their biggest lead to stopping a large scale terrorist attack on American soil. But in the next episode of "24: Legacy," the remaining members of the infamous Army Ranger squad that took out terrorist Bin-Khalid will decide to team up to try and recover what they have lost.
The upcoming episode will cover the events from 3 p.m. to 4 p.m. and will feature Carter (Corey Hawkins) and Grimes (Charlie Hofheimer) teaming up to find the terrorist group that's planning a massive attack on America through strategically placed sleeper cells. They almost had their hands on the list of these inactive spies and terrorist agents, but Grimes' greed for money and the luxurious life he felt he deserved as a former Army Ranger gave the terrorists a chance to nab the list away.
However, it seems that Grimes will try to make amends by giving his former squad leader, Carter, significant information that might just lead them to the terrorists before the sleeper cells are activated. But can Carter really trust his former squad mate?
The trailer for the next episode also shows the CTU headquarters getting compromised when what looks like an electromagnetic pulse (EMP) bomb takes down their computers, effectively cutting off their access to the outside world. Could this really be the beginning of the apocalypse that the late Bin-Khalid promised? And more importantly, who slipped that bomb into CTU's main floor?
The episode will also cover the events at the Donovan compound, where Senator Donovan's (Jimmy Smits) campaign manager, Nilaa (Sheila Vand), is sequestered and questioned for allegedly leaking information about the Army Rangers to the terrorists. Viewers of the series are already aware that she is just being framed for this particular deed by Donovan's father, Henry (Gerald McRaney). However, is she really as innocent as she claims to be? How will she be able to prove it?
"24: Legacy" season 1 episode 4 airs on Monday, Feb. 20, at 8 p.m. EST on FOX.