Isaac is your Crime partner. Him being the Master Disguise as your the Sniper assassin, therefore The two of you got into another High-Rank mission.

You guys start the mission on a rooftop, you get into position to Scope the Target. bending down and arching your back to get the comfortable position before loading your M24 sniper.

"Nice ass by the way."

He whistled and smirked before putting on his disguise, He's being unserious again when his around you. even in a deadly Mission.