"The Scorpion and the Toad" is the second episode in the second season of the television series How I Met Your Mother and twenty-fourth overall. It originally aired on September 25, 2006. The title references the fable of The Scorpion and the Frog, where a frog carries a scorpion across the river, only to be stung before they reach the other side drowning them both. In explanation of his actions, the scorpion states, "It is my nature". This relates to how Barney keeps stealing Marshall's conquests throughout the whole episode.
At MacLaren's, Barney notices Marshall looking at Robin's rear, which makes him and Ted excited as Marshall seems to be getting over Lily. Barney insists on taking Marshall out to meet women. The first time Marshall tries to talk to a woman he fails horribly, talking awkwardly about sweat, and Barney intervenes but ultimately goes home with the woman. Even though Marshall initially refuses to go out again, Barney convinces him to try again and teaches him his “Rules of Mating without Dating”. Attempting to use one of the rules, Marshall approaches a woman and tries one of Barney's techniques, but quickly admits that he just got out of a long relationship and doesn't know what he is doing. The woman actually finds Marshall's admission charming and the two begin to chat, but Barney introduces himself and then proceeds to take her home. Barney convinces Marshall to go out with him again, this time to a college bar near NYU. Marshall does meet a woman, who even gives him her phone number, but in the cab ride home Barney steals the number from Marshall. The following day Barney finds Marshall and tells him that the woman he met at the college bar has a twin sister, and invites him on a double date at MacLaren's. During the double date, however, Barney pulls Marshall aside to tell him that he, Barney, has been propositioned by both twins for a three-way. Upset and frustrated, Marshall leaves the bar.
Meanwhile, Lily, recently back from San Francisco, makes contact with Robin, who goes apartment-hunting with her. Robin tells Ted that Lily is back in town and that she seems happy, telling Robin that her art program was amazing and she loved San Francisco because she met such interesting people. Ted reacts badly to the news that Lily is so happy, saying that after dumping Marshall she should feel terrible. Robin convinces him not to be mad at Lily for moving on and they join Lily to continue her search for an apartment. After spending a little time with Lily, Ted tells Robin that he can tell that Lily is miserable and that she is just pretending to be happy. Robin thinks that Lily really is happy with her life, so Ted makes a bet with her, saying that after three tequila shots Lily will tell them the truth about anything. Three tequila shots later, Lily still seems happy and Ted admits that Robin was right, but after Lily receives a call letting her know that someone else got the apartment that she wanted, Lily breaks down and admits that she is miserable without Marshall. She reveals that she lied about her art program—her teacher said that she had no talent—and the "interesting people" in San Francisco was actually one guy with a personality disorder. She asks Ted if he thinks Marshall would take her back and Ted says he would, but warns her that she should only contact Marshall if she knows for certain that she wants to reconcile with him.
Lily goes to find Marshall and runs into him as he is leaving MacLaren's. Lily apologizes to Marshall, saying that going to San Francisco was the worst mistake that she has ever made, and she asks if they can get back together. Marshall says that when Lily broke up with him she broke his heart, but he has realized that she was right, that he does need to find himself outside of their relationship, and that he doesn't think they should get back together, at least at the moment. Saddened, Lily asks if they will still see each other and Marshall admits that he isn't sure. Storming into MacLaren's (at Marshall's request), Lily approaches Barney, still schmoozing the twins, and throws a drink in his face, claiming that he gave her chlamydia. She then returns in a hat, posing as an alleged twin sister, scaring off his dates.