Plot and/or ending details follow.
135 was one of two Squadrons sent by Big Boss to follow Walky on his ill-conceived one-man assault on the Alien HQ, though their first "on-screen" appearance would not come until Monkey Master's attack on SEMME HQ some time later. Jason Chesterfield subsequently encountered Squad 135 in Colorado while pursuing Sal Walkerton, though Sal made short work of them in the ensuing battle.
Squadron 135 was eventually brainwashed by the JFO with Beef's help while on a routine mission in London. When the JFO attacked SEMME under Penny's leadership, 135's members were "triggered" to attack their fellow agents. Squad commander Daisy killed Mandy, as well as standing by and allowing Penny to shoot Grace before fatally wounding Grace herself while shooting at Walky.
After being freed, shaking and crying with anger over this, she shot Beef in the head, killing him, and then kept shooting him until her handgun ran out of ammo. The surviving squad members were then placed in temporary incarceration with the other victims of the JFO's mind control plot.