When you reach the house with the red smoke it turns out to be one of Rais' chemists - who is cooking up dope and needs his shopping list filled. He gives it to you with instructions to deliver it to his contact - but that is a mistake.
You radio the Tower and listen while they cook up their own plan to deal with this. You need to fill the shopping list - but bring the stuff to the Tower!
Head to see Aziz at the Bazaar first, then head to the tunnel to get the chemicals from the car.
Once you have the chemicals head back to the Tower and meet with Aman - he gives you a substitute that will have the opposite effect of the drug that he means to make. Sweet!
So head back to the house with the red smoke and deliver the goods!