As you walk down the hall, you notice that the rumbling noises seem to be coming from another metal door at the end of the hall, but there are two less fortified doors on either side of the hall as well.

14 athletics 

Cass focuses on the door at the end of the hall- tries to open it or bust it open..

Quote from Tesservett >>

14 athletics 

Cass focuses on the door at the end of the hall- tries to open it or bust it open..

 The metal is quite tough, try again.

Tuna will try and unlock it if able otherwise will swing his maul at it.

 Thieves tools 24

Athletics 20 21

Quote from Grakus13 >>

Tuna will try and unlock it if able otherwise will swing his maul at it.

 Thieves tools 24

Athletics 20 21

 Both rolls would work. I assume you just pick it though.

As you open the door, you are hit with a blast of hot air. You see a large metal machine, glowing with orange-red light, and spewing heat and steam.

There are three people inside the room, and a small floating creature obscured by the steam. Roll initiative. 

Initiative 6

nature check to see if I can figure out what the creature is.22

1 

initiative.  

(Do we have a surprise round?).  

Quote from Grakus13 >>

Initiative 6

nature check to see if I can figure out what the creature is.22

 It's a steam mephit.

Quote from Tesservett >>

(Do we have a surprise round?).  

 No, they heard you opening the door, it's very loud and creaky.

Enemy init:

12

3

19

4

A sailor lunges at Tuna with a hatchet.

Attack: 17 Damage: 9

Cass is up.

“Argh!  Surrender or die! “

Cass yells, and blasts the room with a maximized Shatter.   10’ radius =20’ diameter,   She tries to get the machinery, the three sailors and the mephit

24 points of thunder damage-  dc 13 con save for 12.

uses her channel divinity and her last 2nd level slot

12

17

11

8

Two sailors and the steam mephit are instantly killed.

Assuming you were out of range of your own shatter:

6

...aaand the steam mephit blows up and further damages the already injured surviving sailor. You just almost 1-shotted the room, and now it's Tuna's turn.

Tuna grimaces in pain from the hatchet blow to him and tries to stab the sailor with a rapier and as a bonus action bite him with Hungry Jaws.

Attack: 19 Damage: 6

sneak attack if possible 9

and bite Attack: 8 Damage: 3

The last sailor is dead, and the room is still, except for the whirring of the machine.

 Cass turns and closes and locks the door to this room.   she gives guidance to and helps Tuna with trying to disable or turn off the machinery.  
(plus 1d4 and advantage to tuna) 

Tuna sheepishly looks up from stabbing the corpse of the sailor and says " Sorry I  thought I saw this one twitch. I'll get started on the machinery. I doubt I can figure it out but I might be able to make it not work."

Investigation 9 guidance 3

Thieves tools for disable 24

and if all else fails he'll start beating it with a maul.

Athletics 13 3

Tuna, I believe Cass gave you advantage on perception 19+ 1

Tuna manages to open a panel on the side of the machine. Inside, he sees lots of spinning metal shafts, gears, and a glowing red sphere.

“Mayhap we should get that red glowy ball out o there!     We need  Ari or Ceesh here!”  Cass says

Quote from Tesservett >>

“Mayhap we should get that red glowy ball out o there!     We need  Ari or Ceesh here!”  Cass says

 The two of them are waiting for you up on the Stone. 

As you are inspecting the machine, an officer spots you from across the hall and shouts

"WE HAVE INTRUDERS IN THE ENGINE ROOM! PROTECT THE ENGINE!"

He charges down the hall, cutlass drawn.