The Line of Duty

Locate and rescue the missing members of Station 17 Fire Crew. The other firefighters aren't marked in the map. You can try finding them by going up in vantage points while in detective mode. Look for a close group of people surrounding a struggling victim. Thugs who kidnapped the fire crew can be easily identified this way. You can also listen to the radio chatter either by the police choppers or the thugs themselves.

Bleake Island

1. This is the very first firefighter you'll rescue once the mission becomes available. Follow the marker which will lead you to Panessa Studios. The firema is inside the building under a crane. You can use your grappling hook to reach that crane and dive attack the thugs inside from the rooftop glass. Defeat them all and free the fireman.
   
2. This firefighter is located in the northwest corner of Chinatown, in the back alley.
   
3. This firefighter is located in Chinatown, at the back of the building NW of GCPD.
   
4. This firefighter is located in Chinatown, in the middle of the district.
   
5. This one is located in the NE corner backyard of the Falcone Shipping Antenna.
   
6. This fireman is located on top of the crane with some armed guards.
   

Miagani Island

1. You'll find him under the bridge connecting Miagani Island and Bleake Island. (Warning: These guys are armed)
   
2. He is located near Grand Avenue, on upper ledges of the Gotham Herald building. You need to get to an vantage point in a right angle to spot them since structure is covering them.
   
3. Located in the Grand Avenue train station. He's surrounded by turrets. There's no shortcut or vent you can hide to take out the thugs one by one. You need to fight on foot but on the turret's blind side. None of them have any weapon so as long as you stay out of the turrets' range, you'll be fine. Also, you can use smoke pellets to disorient the guards as you disable some of the turrets, especially the middle ones. This is a lot easier if you have the RHD upgrade that will allow you to temporarily disable the optics of an auto-turret, giving you enough time to sneak behind and destroy it.
   
4. This firefighter is located in the SE corner of the Wayne Tower.
   

Founders' Island

1. Located inside the building in the middle of Port Adams.
   
2. Urbarail Station in Ryker Heights. There are three brutes in the area as well a weapon cache where they'll get their weapons from. Disable their weapons first with the Disruptor before diving in.
   
3. This firefighter is found on the elevated walkway NW of the Wayne International Plaza. (South of the airships) There's also a weapon cache nearby. Consider sabotaging it first before engaging the thugs.
   
4. Found in the lighthouse NE of the airships. Detective Mode is jammed in this area and there's also a sniper in the lighthouse. Take out the sniper first then eliminate the thugs.
   
   
5. This last fireman is the hardest to find. First, you have to take the lower road find a Killinger Dept Store establishment. In front of it is a wall that you can pull using the Power Winch. Refer to the map below to know the exact location of the wall.
   

   Get into a vantage point and sabotage the weapons of the two armed thugs, and their weapon crate. If you have upgraded your Fear Multi-takedown skill, you'll be able to take out at least five of them immediately. If possible, try to target one of the guys with the riot shields since you can easily take them out and reduce your problems later.

   
   

After rescuing the last firefighter available, you have to rescue their chief. His location will be marked in the map. Head to Cityvision Construction site. The area is filled with thugs but there are a lot of options and objects for you to play with. Once you took out all the thugs, find the Chief and free him. Next, you have to drive the chief to GCPD to close the case and complete the mission.