Candace panics when she inadvertently agrees to babysit Jeremy's little sister Suzy but to her surprise, Suzy is docile in the absence of her brother, saying that when Jeremy isn't around, she's "off the clock." The two of them bond and Suzy shows Candace how to get Phineas and Ferb to bust themselves. Meanwhile, the boys build a replica of Niagara Falls in their backyard with the intention of riding over the falls in a barrel. Back at Doofenshmirtz Evil Inc., Dr. Doofenshmirtz decides to increase his carbon footprint, (though he doesn't know what that is), by inventing a Carbon Footprint-inator.