Heartstealer

Go to Thessalia's Fine Clothes in Varrock and talk to Thessalia to receive masquerade masks.

Return to Caelyn.

Click the interactable objects in the room. After failing, lower the difficulty setting by speaking with her.

Follow Caelyn's instructions / the arrows to click on the areas of the room to make the smoke bombs.

Finish the dialogue with Caelyn to receive paper and crayons.

Head to the Varrock Museum and pickpocket Curator Haig Halen.

Return to Caelyn.

Head to the Varrock Museum and talk to Caelyn outside.

Wear the Scarlet Thief's mask and talk to Caelyn again.

After a cutscene, attempt to walk-down the stairs, then climb-up the staircase to the east.

Talk to the Drunken Dwarf to the south.

Talk to the Bartender downstairs to get 1 drink token.

Pickpocket an attendee south-west for 1 drink token.

Talk to the masked woman to the west upstairs and accept the dance off.

After the cutscene, talk to the masked woman again to get the 1 drink token.

Talk to Mr Mordaut, the dragon.

Go downstairs and search the crate next to the Bartender to get a cheese tray.

Go upstairs and talk to Mr Mordaut again for the last drink token.

Talk to the Drunken Dwarf.

After another cutscene, go down to the basement.

Avoid the guards, following the wires on the ground to find the levers.

There is one lever in each of the north, east and western rooms. Avoid the guards by blocking their line of sight with objects where possible.

North: Avoid the guards and hide in the crate (halfway along the back wall) to avoid the guard.

East: Hide in the crate (Halfway along the eastern wall) to avoid the guard.

West: Notice the walking pattern of each guard. Then walk directly behind the guards along their route waiting for when they turn away to move.

Pull the three levers.

Open the display case.

After a cutscene, take from the display case.

Talk to Caelyn.

Continue dialogue with Caelyn.

Quest complete!