Episode 317
Viper (master of disguise) shows up on Earth, looking to attack Keroro! And so the platoon leader desperately tries to figure out which person in the Hinata household is him. After that, Giroro gets trapped in Natsumi's upper closet. How will he ever escape without getting noticed?! Source: crunchyroll
Aired 05/06/2010EP 317 - Episode 317
Sgt. Frog
Keroro is a frog-like alien sent from his home planet on a mission to conquer Earth. But when his cover is blown, his battalion abandons him and he ends up in the home of the Hinata family. There, he's forced to do household chores and sleep in a dark basement that was once supposedly a prison cell haunted by the ghost of an innocent girl. He even spends his free time assembling Gundam model kits. During his stay, Keroro meets up with subordinates who were also stranded during their failed invasion.
(Source: Anime News Network)