事に is not placed at the end of the sentence. The full sentence is

あまり物騒な事に首を突っ込んだらダメよ

XXXに首を突っ込む is a set phrase. It means "to meddle into something." It is almost equivalent to English's "poke your nose on something that is none of your business."

You can understand the sentence as

It's bad to excessively poke your nose on dangerous things.

事に is not placed at the end of the sentence. The full sentence is

あまり物騒な事に首を突っ込んだらダメよ

XXXに首を突っ込む is a set phrase. It means "to meddle into something." It is almost equivalent to English's "poke your nose into something that is none of your business."

You can understand the sentence as

It's bad to excessively poke your nose into dangerous things.