Your query should hook, interest and fascinate the agents enough that they want to read more.
If your tagline does that, great. If your tagline is just there dangling like a piece of unwanted sanitary string just because "I've got to have tagline, because they say so," then you're going to confuse and irritate the heck out of everyone.
Basically, a tagline should evoke this feeling: "Oooh, this sounds so cool/exciting/fascinating/unbelievable. What really is the story about? Let's read on" and not "Duh, don't tell me something before you make me care" or "I'm bored already."