"Growing Pains" and "K-9 Crusader" are the two segments that make up the 29th episode of Krypto the Superdog.
Mechanikat shows Snooky his new laser beam that makes a plant grow, and will turn Krypto into an old dog. Meanwhile, Krypto plays basketball with Kevin, and Kevin laments he cannot reach the basket without Krypto's help. Then, Krypto hears Snooky's ship and goes where it is with Kevin. Snooky shoots the ray to Krypto, but it first bounces and hits Kevin, then a second ray hits Krypto and turns him old. After Snooky leaves, Krypto sees Kevin has become an adult.
Snooky returns to Mechanikat's ship to announce his success, so Mechanikat can proceed with his plan. Kevin returns home and Andrea comes to visit,so Kevin dons his father's clothes and pretends to be an uncle. To not find any other unexpected visitor, Kevin and Krypto go to Krypto's ship and watch the news about the biggest yarn ball, which must be Mechanikat's target. The old Krypto tries to stop the villains while Kevin goes after the ray machine. Krypto is too old to stop them, but Snooky accidentally cuts a thread with his claws, so Krypto pulls the thread to recover the ball and Kevin gets the machine. Kevin turns Krypto back to normal and before being turned back himself, Kevin takes the chance to put the ball in the basket now that he's taller, then he's turned back into a kid.
Ace and Krypto pursue Bud and Lou, who hide in a sewer. The heroes are about to find them until they see the Bat-Signal. When they reach the source of the sgnal, it turns out to have been sent by a dog actor who wants to study Ace for his future role in "K-9 Crusader", which Ace grudgingly accepts. The actor follows Ace and imitates him, so when Ace catches a thief with his rope, the actor also throws a rope that ends catching Ace and freeing the thief.
When the actor finds a poster about the Mona Leash at the art museum, he tears it to se a poster from his old films, and the poster clues Ace to find the Hyenas at the museum. Ace and Krypto enter the museum while leaving the actor outside, but he gets an idea to help and takes out his make-up kit. The heroes find the hyenas about to steal the Mona Leash; the hyenas throw a gas bomb but Krypto disperses the gas with his super-breath. Bud trips with a dinosaur skeleton but before Krypto reaches him, he throws a valuable bone to distract the hero, who has to rebuild the skeleton. A "Bud" reunites with Lou and they push the sacophagus of the egyptian exposition to make them fall as domino pieces, so Ace has to hold them until Krypto arrives. "Bud" takes the painting and tells he'll follow Lou, but when Lou runs, "Bud" takes the opposite way. The actual Bud reaches Lou and asks where the painting is, and they are caught while arguing. The fake Bud reveals to actually be the actor who disguised himself to recover the painting. At the end, Ace and Krypto watch the "K-9 Crusader" movie.