What's the scam?

What's going on? What are you trying to pull? Said when one is suspicious of someone else. A: "Why would you be afraid of talking to the police if you haven't done anything wrong? What's the scam, Mr. Thompson?" B: "Nothing, I swear! Police officers just make me nervous, that's all."

Farlex Dictionary of Idioms.

What's the scam?

and What's the deal?

Sl. What is going on around here? (Often implies that something seems to be wrong.) There's a big rumpus down the hall. What's the scam? I gave you a twenty, and you give me five back? What's the deal? Where's my other five?

McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

What’s the scam?

and What’s the deal?

interrog. What is going on around here?; Explain what is happening or what you are doing. What’s the scam? What’s happening, dude? I gave you a twenty, and you give me five back? What’s the deal? Where’s my other five?

McGraw-Hill's Dictionary of American Slang and Colloquial Expressions

See also:

cut (one) off at the pass
cut off at the pass
cat around
not trust (someone) as far as (one) can throw (them)
not trust someone as far as you can throw them
not trust (someone) farther than (one) can throw (them)
on the watch
on the watch (for someone or something)
something is rotten in (the state of) Denmark
something is rotten in the state of Denmark

词组	What's the scam?
释义	What's the scam? What's the scam? What's going on? What are you trying to pull? Said when one is suspicious of someone else. A: "Why would you be afraid of talking to the police if you haven't done anything wrong? What's the scam, Mr. Thompson?" B: "Nothing, I swear! Police officers just make me nervous, that's all." Farlex Dictionary of Idioms. What's the scam? and What's the deal? Sl. What is going on around here? (Often implies that something seems to be wrong.) There's a big rumpus down the hall. What's the scam? I gave you a twenty, and you give me five back? What's the deal? Where's my other five? McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. What’s the scam? and What’s the deal? interrog. What is going on around here?; Explain what is happening or what you are doing. What’s the scam? What’s happening, dude? I gave you a twenty, and you give me five back? What’s the deal? Where’s my other five? McGraw-Hill's Dictionary of American Slang and Colloquial Expressions See also: cut (one) off at the pass cut off at the pass cat around not trust (someone) as far as (one) can throw (them) not trust someone as far as you can throw them not trust (someone) farther than (one) can throw (them) on the watch on the watch (for someone or something) something is rotten in (the state of) Denmark something is rotten in the state of Denmark
随便看	as fresh as a daisy as from as from (something) as fuck (as) full as a goog (as) full as a tick (as) funny as a barrel of monkeys (as) funny as a crutch (as) funny as a fart in a spacesuit (as) game as Ned Kelly as game as Ned Kelly (as) gaudy as a butterfly (as) gay as a three-dollar bill (as) gay as pink ink as gay as pink ink (as) gentle as a lamb as good as as good as... (as) good as dead as good as done (as) good as finished (as) good as gold as good as gold as good as it gets (as) good as new