Nick is in pursuit of finding out how to build a drawbridge. In Spansylvania, they meet a dragon who's in pursut of them - and along the way they find out that some materials are better suited for bridges than others. / When Nick and Sally's boat sinks, a trip to Floating Island helps them discover that along with needing the right material, you also need to make the shape of your boat float.

When Sally destroys Nick's model of a mountain, the Cat takes them to meet Sara of Serendip, an inventor who helps them understand that you can make new discoveries through your mistakes. / Nick discovers that Sally can't hear him when he yells from his bedroom window if their bedroom windows are closed. The Cat takes them to the Soundy Sea and they learn that sound travels in waves.

Sally finds out about a force called friction. Then the kids learn about pulleys and simple machines.

When Nick loses Sally's bouncy ball, they go to Ballaballo to learn about how different balls are made of different materials. Later, during a sleepover, Nick learns about shadows after being scared by one.

Nick and Sally need a strong piece of string to pull their train, but it breaks. The Cat takes them away, but the TMJ malfunctions and they have to make an unscheduled landing. / Nick and Sally notice a bird flying back and forth in the tree branches. The bird is building a nest and they want to get a closer look. The Cat takes them to a mirror world where they learn how reflections work.

Nick is startled by a shadow during a sleepover in the treehouse.

Sally tries to fly a kite but can't seem to work out the timing with the wind.

Nick and Sally are frustrated by a puddle that always forms at an inconvenient spot on the sidewalk. They go to a water park and learn that water always seeks the lowest level. / Nick wants to create a new home for the cricket in their backyard. The Cat takes them on a journey but has to make an emergency landing on Lagoona-Maroon where they discover what they really need when making a shelter.

Sally is trying to make a vase for her mother but each one she tries falls over. Cat takes them to Blueprintia and they discover what they can learn by designing before building. / The kids are creating a game that involves "fishing" for prizes, but they can't "catch" any of the prizes. The Cat takes them to an arcade where they discover what will and won't be attracted to a magnet.

Sally plays a song on an instrument, but can't seem to find the right note.

Sally keeps getting found when they play Hide and Seek. Cat takes them to Tagaloo to meet a great seeker. Along the way they find out that they can use of more than their sense of sight to find things. / Sally loses her special bead in the sandbox and they can't find it. Cat takes them to the Hole-Lot-of Funhouse, along the way they discover how filtering works.

Nick's magic trick causes his toy car to disappear under the porch.

Nick and Sally try to save a bubble for Sally's mom.

Nick and Sally are playing musical instruments and notice that Fish's water is rippling. Cat takes them to the Jingly Jungle for a concert by the great Vibrato. They discover that sound and vibration go together. / When Nick's water glass falls over without anyone touching it, Cat comes to help them solve the mystery. They go to The Great Causeway and discover the world of cause and effect.

Sally and Nick try to add extra bits to Nick's toy glider to make it fly farther. But the more elements they add to the toy glider the worse it flies. They learn that adding too much to something that already works can make it work less well.

When Nick drops the mail bag into his train set, his fingers are too big get it out. Cat shrinkamadoodles them so they are small enough to be in the train set. But when the Thingamajigger falls out of reach, they need the right sized tool to help them out. Sally thinks that the three stick she has are not enough to make anything.Cat takes them to a place where they can get more sticks. And along the way, they discover just how many things you can do with three sticks.

Sally is convinced that a tall thin glass of juice holds more than a short wide glass so Cat takes them to Point O'View where they learn that getting evidence can cause them to change their mind. Nick and Sally wonder if they can walk on a cloud, and the Cat takes them to Mount Knowmore. As they climb up, they discover hard surfaces and watery surfaces and walk through fog. And when they get to the top, they know more about walking on clouds.

Sally invents a secret treehouse handshake, but Nick cannot remember the sequence. Cat takes them to Over-and-Overton, where they figure out how to get through a series of obstacles by recognizing patterns. Nick and Sally do not understand why one toy car goes faster than another. The Cat says he needs their help to move some big pictures and along the way, they find out about how to make things more aeordynamic.

Nick and Sally are disappointed when their toy's battery runs out of power. The Cat takes them to Lots-o-Lakes Land to see the flight of the Dipsydoodlers. But along the way, the Thingamajigger runs out of Go-Go-Go juice and they have to find other ways to make it go. Sally and Nick have wrapped Father's Day gifts, but when they get mixed up the kids cannot tell which is which. Cat takes them to Zippy Zaroo's Cookie Factory where each cookie has a toy inside. When the shrunken Thingamajigger ends up inside a cookie, they have to figure out which cookie it is in.

Sally wants to make a perfect mobile with four identical rubber ducks, but she has only three ducks. The Cat takes them to The Bazaar at Balancia Point, where everything is in balance and has to remain so. Sally finds out there is more than one way to balance things. Nick and Sally are trying to build a sandcastle but the sand is either too dry or too wet. The Cat takes them to see the Song Flower Sisters, who need just the right mixture of water and soil before they will sing.

Sally can't stay hidden for long during a game of hide-and-seek.

Sally loses her special bead in the sandbox.

Nick's magic trick causes his toy car to disappear under the porch.

The kids want to make a great snowman.

Nick and Sally can't agree on how to sort their toys.