To be “in for a treat” means to be guaranteed to receive or experience something unexpectedly pleasant or beneficial.
“You are in for a treat” is an idiom that means you are going to enjoy something. For example, you might say “You are in for a treat!” if someone is about to see a movie for the first time.
Examples in a sentence
“If this is your first time listening to Plain English, then you're 'in for a treat'”.
“The city will be 'in for a treat' when the new show opens there”.
“We're in for a treat! We will have great pleasure! We're going to enjoy this! This will be a delight for us!”.
Explanation
The word “treat” can be used as a noun to mean a pleasure, delight, thrill, or luxury. It can also be used as an idiom in British English to mean very well or very good. For example, you might say “The plan worked a treat” or “The food was delicious; it went down a treat”.