Smarts is the faithful canine companion of Mighty Mikey Power: Kid Detective! Or, rather, he was before Mikey lost his taste for detective work...
As his owner Mikey Power took on the case of locating Annie's stolen bicycle, Smarts was able to find a set of foot prints Mikey believed could lead them straight to the culprits. After neighborhood bullies Finney and Pidge kicked Mikey around a bit, leaving a muddy footprint on his face, Smarts tried to give his master a sympathetic lick but was stopped by Mikey, who didn't want him tampering with potential evidence. And for good reason too, as that print on his face was just the piece of evidence that Mikey needed to identify Pidge as the thief! As the bully got a talking to from a police officer, Smarts joined Mikey in celebrating another cracked case.
Later, Smarts accompanied Mikey and Pidge as they investigated the "haunted house" Finney had gotten himself trapped inside of. Though Pidge was quickly scared off by a "ghost", Smarts and his master knew there was no such thing as ghosts and found the spirit was actually being created by a mysterious "hologram projector". After British special agent Action Man stopped the smugglers hiding out in the house from getting the drop on Mikey and his dog, Smarts sniffed out where the criminals were keeping Finney hostage, leading to his rescue. After this incident, Mikey lost interest in his detective work and became obsessed with unlocking the secrets the hologram projector held. This obsession led to Mikey neglecting Smarts in favor of his research, leading to the dog running away from home.
Decades later, as the adult Mike Power began dying after shutting off his atomic body, he reflected back on his childhood and apologized to Smarts, wishing that they could have had one more winter to spend together.