The photos in the slideshow below look fairly innocuous.
That's because you don't see what's lurking around the corners of the sewers that Barry, Joe and Cisco are exploring is big ole Gorilla Grodd, who has been set loose on Central City to distract Barry and his team from keeping the Reverse Flash from making good on a threat he made against someone. But who?
In The Flash Season 1 Episode 21 Joe will come face-to-face with Grodd who will utter "No help here," when he kidnaps Joe in the tunnels. Will Grodd keep the upper hand or will good triumph?
Elsewhere in "Grodd Lives" Barry and Iris will have a heart-to-heart talk. Whether it's about her love life, their friendship, her father getting into trouble working with The Flash or one of many other possible topics, we'll just have to wait and see.
We have to take a moment and talk about how cute Cisco looks in the photos in his little hard hat. Of course he has safety in mind!
The installment will air on May 5 at 8/7c, so be here shortly afterward for a full review.
If you need to do some catching up, you can watch The Flash online right here via TV Fanatic.
Carissa Pavlica is the managing editor and a staff writer for TV Fanatic. Follow her on Twitter.