Drew plays a practical joke on Stu, where he unwittingly hurt Grandpa with his newest invention, a robotic bee. This inspires Angelica to play a practical joke of her own on the Rugrats, setting it up so that they would think that Dil pulled these jokes. All this goes on while the Rugrats play a King Arthur adventure.

After Didi has hided the cookie jar from Angelica, Angelica has threatened the Rugrats with her starvation if they don't find the cookies in time. Their mission becomes a prehistoric fantasy, where the Rugrats, now ""cavebabies"", find Dil, the ""Wise Cave Baby"", so he can point them in the direction of the cookie jar, or, ""Cookiesaurus"".