M1 - Cashing in Old Favors is a mission in Deus Ex: Human Revolution.
Meet Sarif in the PenthouseEdit
This is a brief story-only mission between leaving Detroit for the second time and arriving back in Hengsha. It takes place entirely in Sarif HQ. There are a few additional messages to be found on terminals, and some previously hacked terminals have been locked again. Most of the area is unchanged from your previous visit.
Take the elevator up to Sarif's office to find Hugh Darrow waiting for you. After a brief exchange Sarif returns and talks to you briefly before sending you on your way.
There is a hidden storage area in a corner of helicopter pad locked by Level 5 security door, by that time you should be able to hack it. If you don't want to hack the lock or your skill just isn't high enough, use the access code, 8053. Inside there is some ammo and Ammo Capacity Upgrade, Shotgun Burst Upgrade.