A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

in on it • on it
in on it—(also: in at it) taking part in an activity; involved
in smth.: We’re sure of one thing — it wasn’t a one-man job.
But were there two, three, or four of them in on it?
on it—
1
. (U.S. sl.) well able to do smth.; in control of a sit-
uation or a task: You bet he could cook. He was just on it. 2.
(Austral. sl.) drinking heavily: When he was on it, and wanted
another drink … he never had to press the bell, but pressed
the button with a bullet.
in on something • on the in with something
in on something —know smth. that isn’t common knowledge:
As Tommy, who was in on the plot, kept Maranzano busy in
the office, the killers disarmed his bodyguards.
Note: 
The expression does not correlate in meaning with the
phrase in for something— used of smb. due for a promotion,
punishment, etc.: That gentlemen is in for a rude surprise some
morning soon.
on the in with something —(U.S. coll.) well familiar with
smth.: Any more information would be appreciated as I pride
myself being on the “in” with Matthew’s films.
in on the kill • on the kill
in on the kill —(also: in at the kill) present at the downfall
of smth. or when smth. dramatic happens: Congress was due
to defeat the bill, and I went to Washington so I could be in
on the kill.
on the kill —(of an animal) having the intention of killing
(as for food): The bison carcass was on this side of the river
in some gravel. A grizzly was on the kill…
in one’s bones • on one’s bones
in one’s bones —(coll.) know or feel smth. instinctively, with-
out proof: I knew in my bones that he was altogether too
obviously foreign to be of any interest to me.
on one’s bones —(NZ sl.) hard up; destitute (also: on the bone):
Ronny Dancy’s on his bones again, I’m afraid.