the once-mighty Kite, put in his arm
it wasn't two months before he'd pawned the D.E.C. and put it in his arm, and had become such a steeply-downhill-type Dilaudid-addict that when he signed on as Gately's new trusted associate for B&Es after Gately got out of Billerica the once-mighty Kite wasn't even able to dicky an alarm or shunt a meter, and Gately found himself the brains of the team, which it was a mark of his own high-angle decline that this fact didn't make him more nervous.
Context
The disease's talent-erasure timed to the month: the crew's chemistry genius pawns his beloved hardware, puts the proceeds in his arm, and inside two months can't defeat an alarm he could once build. The quiet horror is in the last clause — Gately becoming "the brains of the team" by default and being too far into his own decline to find that alarming — two men measuring their descent by each other, each too far gone to be scared by the evidence.