Lisa accidentally sends Lincoln to other dimension.
Lisa is upgrading the portal that appeared in 'One of the Boys', adding to it the capacity of transport to other dimensions and places. First uses a real Guinea pig to test it. She sends it to Taiwan. After a couple minutes, she brings it back. The Guinea pig returns with a bucket of soup, and a traditional hat.
Lisa wasn't sattisfied of the result at all. In that moment, Lincoln was walking on the hallway drinking a soda. Lisa pulls him with a stick, and pushes him to the portal, supposedly with destination to Laos. But she realizes that he won't got to Laos because when she presses the button for go back home, there's nothing out the portal.
Lincoln lands in a distint dimension. When arrives, he sees a conjoined yellow cat and dog, running away from a giant scissors. When he tries to touch them, these fade in blue dust.
Meanwhile in the Loud dimension, Lisa tries to make Lincoln return. But instead of Lincoln, who returns is CatDog, asking what he's doing there. Lisa believes that is cientifically impossible (and it's), a nature mistake (and it's), and something who doesn't have to exist (and you guess... wrong, it has).
Lisa runs to the living room to advice the others about CatDog's existence. All the sisters are amazed, due the mentions I already did. Meanwhile Walt and Geo don't look affected by CatDog's existence, Charles and Cliff are confused. How the heck they go to poop? they ask. In that moment CatDog has to do his necesities, so he runs to the Loud's bathroom. Only screams are heard. After flush the toilet, CatDog has a paper in his stomach, what implies they have a slot in his midriff (yes that, don't be dirty thinking that... um... you know).
Back in CatDog's dimension. Lincoln asks how he did that animal fade. All the inhabitants of the dimension believe Lincoln is a murderer, so they run away the place. In that instant Lincoln is asking for go back to his dimension.
Meanwhile, CatDog is eating. The sisters ask Lisa to end fixing the holy portal, to send back the phenomen to his dimension. A broken jar is heard in the living room. Dog has digged a hole to keep a bone on the pot. Meanwhile five of the sisters chase him, the others try to help Lisa with the portal. After six hours of work, Lincoln finally is back. Now they have to catch CatDog to send him back to his dimension.
After a chasing that destroyed half city, they finally catch him. In that case, the Louds put him on the portal and goodbye. They wished to have photos of that specimen.
This is a crossover. "CatDog" was featured in the episode.