If the Dragonborn has one of the Aetherium items (Aetherium Crown, Shield or Staff) in his or her inventory, Taron will ask how this item was obtained. He will attack no matter which option is chosen in the dialogue.
If the Dragonborn has no Aetherium items, Taron does not ask about them, but if dialogue is engaged with him he may be asked who he is and told that Katria had mentioned him. He will respond with "You know too much," and attacks the Dragonborn with his three mercenaries.
He may also appear with his three mercenaries in the Silver-Blood Inn. The same conversation as above is automatically initiated when you enter the inn. All of the five or so other men in the inn join in the fight on your behalf (the ladies will run and hide), but take care, as your 'helpers' are easily killed in the battle.