Chase the Apothecary through the streets, completing both challenges and tackling him.
Assassin's Creed: Unity guide - Sequence 7 Memory 2: Meeting with Mirabeau - Apothecary
Don't worry about either of the optional challenges until the final objective.
- Slide under or over five objects
- Use one lift
Speak to Mirabeau
This mission takes the form of a murder mystery, which you may have experienced in a side story. It's a pretty straight forward one, though, as long as you complete every green objective before accusing anyone. First up, just heady into Mirabeau's house and go up the stairs to find his room.
Investigate the Crime Scene
Switch on Eagle Vision and find the three pieces of evidence you need to proceed and interact with them. You need to check out the book on the desk, the bed, and the cabinet. You can also look at a handkerchief and speak to Elise, but it's not required at all. Be careful not to accuse Elise trying to talk with her; I don't trust her as far as I can spit, bit I'm pretty sure she didn't do it, for reasons which will become apparent.
Speak to Master Quemar
When the objective updates, trot down to your HQ and enter the council chambers to chat with Quemar. Once you've extracted some information the option to accuse him becomes available - it's tempting, but don't do it.
Speak to the Apothecary
This would be a lot more fun if all the people you need to talk to weren't so far away. You'll be joined by Elsie just before you enter the apothecary, and her doubt in Arno's investigative abilities proves to be well-founded when a cutscene triggers.
Tackle the Apothecary
It's time to do your optional challenges. Don't miss the two slide opportunities in the tunnels. When the apothecary slams a door, don't be tempted to slide over the window to the right - you'll be thrown off course and either have trouble keeping up or end the chase far too early. Instead, veer right at the window and take the lift to reach the rooftops - here you can slide over a number of chimneys as you follow the apothecary's erratic path.
You'll catch the apothecary in a park, so if you don't have your slides done by then do a quick lap and get a few done over some benches - but don't tarry too long, as you may risk mission failure. Tackle the apothecary when you've finished to complete the mission; a cutscene gives you the information you need to track down the real killer.