Create an opening line for the following story.
Plot: A group of secret agents have infiltrated a castle in search of a hidden treasure.
"In the shadow of the night, a team of highly skilled agents covertly entered the ancient castle, determined to uncover its hidden treasure at any cost."
Complete the following task based on the instruction and optional input provided.### Instruction:
Create an opening line for the following story.

### Input:
Plot: A group of secret agents have infiltrated a castle in search of a hidden treasure.

### Output:
"In the shadow of the night, a team of highly skilled agents covertly entered the ancient castle, determined to uncover its hidden treasure at any cost."