Rewards: Pounds: 410 (+75), EXP: 250 (+100), Extra: Brass Knuckles - Crow's Strength
Challenges: 1. Steal the plan undetected. 2. Remain undetected (in the factory).
For this memory it's recommended to have some Smoke Bombs in your inventory. This helps significantly with completing the first optional mission task. When you start this mission, follow the syrup drug trader either into the sewer pipe, or alternatively just stay on street level and follow the marker; you'll actually catch him quicker this way, though it's a less spectacular chase. In any case, once you've tackled him he'll tell you where to look.
Make your way to the next marker and scan the area with Eagle Vision to spot the distributor. When he moves to his carriage, sneak to the road and snatch a carriage yourself, then follow him about 200 meters further down the street. Here he'll dismount the carriage and go into an alley. You now have a few options. If you don't care about the optional objective you can just waste all thugs and brutes but this is actually not recommended, considering the two brutes in the backseat of the carriage are level 5 and pack quite a punch.
A better idea is to knife-headshot the driver, quickly hide around the corner at the end of the street, climb the building and wait for the two brutes to come investigate (they are allowed to see you, it's just the distributor that cannot see you at any time, though you cannot kill the distributor either and then snatch his pocket - this doesn't count).
When the distributor returns, quickly throw a Smoke Bomb at him, rush over and snatch the information from his back pocket, then be on your way to the factory it indicates.
Move to the far side of the factory, where a brute is patrolling. As soon as he turns his back on you, assassinate him. Use Eagle Vision to mark everyone. There's a nearby thug that you can headshot with a knife (or alternatively ignore). When the distribution boss moves up to the second level, scale up the walls in that direction and wait for him to move on the catwalk; approach him from the back to kidnap him. Now simply move out of the factory the way you came and interrogate him when you're out of the enemy territory.