An EGG-sighting Adventure! (めいたんていジュンサー！きえたタマゴのなぞ！！ Detective Jenny! The Mystery of the Vanished Egg!!) is the 20th episode of Pokémon: Master Quest.
With a new egg in tow, Ash and co. have their sights set for Mahogany Town. They stay the night at the local Pokémon Center but the next morning Ash's Egg is gone. Who could be responsible for this? And why does Officer Jenny think it was Brock who did the deed?
Ash is glad to have the egg, while Misty admits it is hard to wait for the egg to hatch. Brock asks Ash which Pokémon type he hopes for. Ash tells as long as it is healthy, it is fine by him. Misty thinks he behaves like a mother than a trainer, but Ash admits he will wait longer to hatch. Team Rocket heard about the egg, so they believe it can be a Legendary Pokémon, like Moltres, Artiuno or Zapdos. James suspects it may be even something to be eaten with ham and sausages. Nevertheless, Team Rocket are ready to snatch it. Suddenly, the clouds gather (making Pikachu pleased). With a lightning blast, the heroes run for the Pokémon Center. Team Rocket were hit by lightning, as their machine attracted the lightning.
The heroes came to the center. Brock tries to flirt with Joy, but Misty pulls his ear off. Joy shows them their room for the night. When the heroes turned the lights off, Team Rocket sneak inside, though Wobbuffet scares them by yelling out. After shushing Wobbuffet, they open the twerps' room and see the egg in the case. After binding Meowth to a rod (who is not pleased about it) they enter the room, but start bickering whose egg will it be. Togepi wakes up and begins to wave hands, while Brock yells to stop, as he swore love to someone else, making Team Rocket intense. Togepi's Metronome teleports the egg away. Team Rocket notice the egg is gone, then see Wobbuffet eating an apple. They close the door and go to the kitchen. Team Rocket are happy, but Meowth warns them they make too much noise. After tripping over Wobbuffet, they shush each other.
Meanwhile, a baby Kangaskhan sees the egg and pushes the case over. The older Kangaskhan yells out and with no reply, places the egg and the baby in her pouch. Ash dreams about an egg, but gets shocked as the egg gets smaller and smaller, then vanishes. Ash wakes up and goes to see the egg, but is terrified to see it gone. Misty wakes up and Joy visits them, so Ash reports the theft. Team Rocket ate a lot of food and leave the Center, with a lot of rubbish. Jenny immediately comes and Brock goes to flirt with her, but Misty pulls him off. Ash tells what happened, so Jenny understands, since she is also a detective. Jenny already thinks of the number of the case: it is #26, the case of the vanishing egg and the fate of beautiful Nurse Joy. Ash sees Chansey and thinks one of them might've took the egg by mistake, so Joy brings all the Chansey. However, none of them have the egg. Jenny sees there must be a clue, so sends Growlithe, to help in the search.
Growlithe sniffs Ash and runs off. Since they are occupied with the search, Team Rocket go to get more food. Growlithe found the egg case, so it is possible the thief dropped the case. A bush shakes, so Ash finds a bunch of Exeggute. Tracking them down, the heroes find a nest, but no egg. The heroes go to check their room, which is what Jenny wanted to suggest, while Brock continues to flirt with Jenny. Seeing that there was no forced entry at the window nor the door, Jenny accuses Brock stole the egg. She thinks it is him or Misty, since Ash is the victim and all three were in the room when the theft happened. She thinks that Brock was lonely as he had no egg. So, she believes that he snuck into the night and took Ash's egg, even if it is immoral. Brock admits he couldn't control himself. However, he realizes he never stole the egg. Ash and Misty are certain Brock would never steal eggs.
Team Rocket are full from the food they have eaten. As Jenny takes Brock away, Misty notices the door knob being damaged. Jenny thinks Brock damaged the knob to make it seem someone else did it. Brock thinks he may have done it, but Joy takes them to the outside door, where there is another scratch. Jenny sees there was someone from outside wanting to break in. Brock is relieved that he is no criminal, while Jenny sends Jumpluff. It uses Spore, which reveals footprints in the room. However, they cannot determine when the thief came. Still, Jenny analyzes the back of the heroes' and Joy's shoes and notices they are not the same. Also, there were two thieves, who did not come exactly near the egg. Jenny thinks they had long arms, while the heroes believe they had a Pokémon to do the stealing, one that can use Vine Whip. Jenny accuses Ash to be the thief since he has a Bayleef that can use Vine Whip, but Misty reminds her he cannot be the thief, plus there are strange footprints.
Jumpluff uses Spore to detect more footprints. Jenny thinks they belong to a Suicune or a Wooper, but the heroes don't think so and follow the footprints. The heroes notice faces of Team Rocket, who wake up in the kitchen. The heroes break in, though Team Rocket escape the building. They follow the footprints and encounter a Kangaskhan, who has Ash's egg. Ash tells Kangaskhan that is his egg. Kangaskhan sniffs the egg and Ash, seeing they both smell the same. Ash obtains the egg back, but Brock wonders how did she have the egg if Team Rocket took it. Jenny thinks that Kangaskhan challenged Team Rocket to a battle and won, receiving the egg. The heroes thank Kangaskhan, who is confused, while Team Rocket observes the situation. Soon, Team Rocket uses a robot arm to take the egg.
Jessie sends Arbok and James Victreebel, who gnaws on James. Arbok goes to attack, but gets hit by Kangaskhan's Dizzy Punch, confusing it. Jenny sends Growlithe, whose Flamethrower burns away the hand, causing the egg to fall down. Ash catches the egg, while his Pikachu blasts off Team Rocket and their balloon. Jenny praises Kangaskhan, as her help got the egg back to Ash. Jenny admits this was a tough case. Brock tries to flirt with Jenny, but Misty pulls his ear away. Ash thanks Joy and Jenny for the assistance, who bid farewell to the heroes. Brock admits it is a tough egg, since it overcame Team Rocket's scheme. Misty thinks it could be a Psychic-type, but Ash will be pleased when it hatches.
The "Who's that Pokémon?" is Blissey.
When Ash realizes his egg was stolen, Misty's ponytail was missing.