An unknown terrorist has planted bombs in public places in Sydney causing a large amount of injuries. While Sierra Alpha treat the wounded the police are on the trail of the bomber.
The terrorist cell is identified and with the kidnapping of a prominent politician a deadly hostage situation begins. There are other bombs placed around the city but will they be found in time.
A group of hiking tourists have not reported back as per their plan and are regarded as missing in the Wollemi National Park. Rescue 21 joins the aerial search. A fire in an industrial unit pushes the resources at Sierra Alpha to their limit.
An out of control delivery van hits a group of pedestrians and it's proven that the driver had been taking a tainted medication. The search is on for anybody else prescribed the drug.
While delivering urgent medical supplies, Rescue 21 loses power and has to commit to a rough landing in the middle of nowhere Injuring Stella in the process.
Engine 045 responds to a fire at a care home that appeared to be set deliberately. Sierra Alpha receives victims from a severe case of food poisoning at a political rally. Was it intentional?
A pregnant woman is brought into Sierra Alpha in distress and the doctors are forced to deliver the baby early to save its life but the mother doesn't survive. The father swears retribution on the hospital.
Rescue 21 is called to rescue a family from their leisure boat as they've all fallen ill. After transportation to Sierra Alpha it becomes clear that the illness is caused by a highly communicable disease, but which one?
Sgt Warren and his team are called to a bank robbery but the robbers escape in a vehicle after one of them has been shot. They kidnap a doctor to help the wounded member.
A fire in a factory reveals a sweat shop crewed by illegal immigrants. No escape route forces engine 045 to break in to rescue the workers while trying to stop the fire spreading to adjacent buildings.
The gang have made it clear that they want control of the city and start burning business that won't cooperate, injuring staff and anybody who gets in their way, and firing on police.