Meet Darn Cat (DC), a playful Siamese tomcat who rules the roost in the Randall household, which is home to sisters Ingrid and Patricia. By night, DC embarks on whimsical escapades around town, amusing himself by teasing local dogs, snagging snacks, and leaving his mark on unsuspecting vehicles.
One fateful evening, driven by his curiosity, DC follows the notorious bank robber Iggy into an apartment where Iggy and his accomplice Dan have taken hostage Margaret Miller, a bank employee. Seizing a moment of chance, Miss Miller cleverly switches DC's collar with her watch, desperately inscribing letters to spell "HELP" amidst a flurry of worry.
Upon his return home, DC's antics continue to unfold. While the Randalls are oblivious to the cat's adventure, Patti discovers the watch and suspects it belongs to the kidnapped woman. Determined to take action, she speaks with Agent Zeke Kelso at the FBI, and thus, Supervisor Newton assigns Kelso the task of tailing DC, in hopes that the clever feline will lead them to the robbers' lair.
Kelso sets up camp in the Randall home, assembling a team to monitor DC's every move. However, the mischievous cat proves too crafty to catch, constantly evading their traps through humorous and embarrassing episodes. The grand conclusion features a thrilling chase that winds through backyards and a drive-in theater, eventually leading to a funny encounter with Gregory Benson, the owner of a pigeon coop, who hilariously chases both DC and Kelso away.
As the operation continues, Agent Kelso's supervisor Newton grows frustrated and decides to discontinue their efforts, claiming the watch to be an unreliable lead. Not one to give up, Patti disguises herself as a colorful niece of her jeweler friend Mr. Hoffsteddar, embedding herself in the FBI's investigation and asserting that the watch is indeed significant evidence. Thus, Newton and Kelso embark on one last surveillance mission from the Randall's home, tracing DC across several neighborhoods until they finally locate the robbers' hideout.
In a thrilling climax, Kelso arrives just in time to rescue Miss Miller, with Patti gallantly following closely behind, determined to protect her newfound hero. After a brief scuffle, the kidnappers are apprehended, and Miss Miller is freed from her ordeal.
After this exhilarating adventure, Patti reconciles with her on-again, off-again boyfriend Canoe, who had been grappling with jealousy due to the secretive nature of the FBI's investigation. Meanwhile, Agent Kelso discovers new love with Ingrid, as DC embarks on a new chapter of his life with a lovely gray cat he has encountered during his nightly escapades.
