When Big is building his latest invention, a Sunshine Catcher, he loses the doohickey that is integral to the machine's operation. He sinks into a deep funk and lay on his bed fiddling with the pieces of a puzzle. Unknown to Big, Small had put the doohickey into his collecting bag of bright, shining objects, totally unaware that it was the actual, important doohickey. Small endeavours to cheer up Big by trying hugs and pulling funny faces and doing some cool dancing. Nothing works. Small then hits on the idea of making Big a cheer-up cake. He's sure that will work. When the cake is baked and iced Small thinks it needs a finishing touch: and he uses the shining doohickey from his collection. When Big sees the cake he sees the missing item and leaps happily from the bed. Result! / Small wants the glorious apple that's hanging from the tree, even though Big tells him it's not yet ripe. But Small looks so sad that Big puts friendship above his knowledge of apples and picks the fruit. But "Yuck! That's not an apple, that's a lemon!" is Small's reaction to the first bite. Big takes a bite himself to see if it really is that sour and recoils with horror when a voice speaks to him from inside his mouth! He has swallowed something that lived in the apple! Small reaches in to free the trapped creature who turns out to be a sassy but warm-hearted worm. She doesn't have a name but suggest they call her Twiba: The Worm In Big's Apple. And now Big and Small have a new friend out in the garden.