Immediately after you accept this quest two large groups of shadow creatures will spawn at the entrances to the temple, trapping you inside. They will start attacking the center platform soon. At first they will come as pairs of Shadow Beasts. Then, they will come as pairs of Abyssals. Make sure the Forgemaster survives. If the attackers are allowed to get near him, he will engage in the fighting. While he can take some heavy damage, he is not listed as an ally in your party, so ensure that a healer watches his health.