Keep the combination with you at all times while doing this quest

Talk to him again and ask if he would like Fallen Earth gold to gamble. Wager around 500gps. Harold will then roll two dice. Your objective is to roll a higher combined number on the 2 dice than he does.

Once you win, he’ll give you back your money and hand you an IOU. Read the IOU to identify that it is the combination (keep the combination with you at all times while doing this quest; you’ll need it at the end).

Head back to the castle. On the ground floor, head to the west corner of the room and pick up the red, blue, purple, green, and yellow stone balls. Then place the 5 items in the correct positions on the Stone Mechanism table to the right. Here is a diagram of where the balls should be placed on the table.

Once you finish placing the last ball, you will get a message saying that the equipment room door was unlocked.

Now go and get 10 cooked trout (trout can be fished in Barbarian Village), 10 bread (either steal them at the stalls in Ardougne or make them at nearby windmills), and an iron bar. From Bur Thorpe, head up northwest towards Death Plateau (follow the northwest trail from the castle).