Carter's plan: they can reprogram Fifi the Wonderdog to sniff out magma. With the help of Dr. Mandle's super mucus, Fifi's nose should be powerful enough to do it. Carol is hesitant at first, but Carter charms her by calling Fifi a heroine.
While Stark prepares the tunneller (you didn't think they would spend all that money on such a huge prop and only use it once, did you?), Carter shoves some hardened lava in Fifi's face to give her the scent. I hope hardened lava smells the same as the fresh stuff. Hood enters the scene to hand Carter a suitcase full of explosives. They're going with Allison's plan since Carter's lance the puppy idea would get them killed. And yet, his other idea will save thousands of lives, so stop talking down to Carter like he's a moron, Stark. Hood watches our brave tunnellers (and Stark) depart. And for someone who's never driven a tunneller before, Carter picks up the skill pretty quickly. I guess if Bebop and Rocksteady could drive one of those things, just about anyone could.
Above ground, Allison nags Stark and Carter to get things done faster, as methane vents are now popping up all over town. Eva and Allison are just standing next to one as if it's a campfire and they can't wait to make s'mores. These people do not take volcanoes seriously enough, I swear. Meanwhile, Hood is having the day of his life. He freaking loves methane vents.
Fifi finally gets a whiff of magma. Stark actually has the gall to look bummed that Carter's plan worked. Yeah, that totally sucks that the entire town -- and your fiancée and, I guess, her son -- are saved. If only they could have all died in a volcanic explosion! Then you would have saved so much face. Meanwhile, I'd like to know why they don't send Tracy down to do this stuff since it's all her fault. Why put innocent Stark and Carter's lives in danger? Carter stops the tunneller. He, Fifi, and Stark get out and take a look around the tunnel. Well, Carter and Fifi are looking. Stark is just lecturing Carter for referring to the magma as "lava." Apparently, you call it magma when it's underground and lava when it's above. I call it "red liquid death" no matter where it is. Carter pretty much ignores Stark, instead focusing on the magma pocket he just found. He may have cut things a little close, since the magma is threatening to burst through the thin wall and into the tunnel any second. Carter, Stark, and Fifi jump back into the tunneller with the explosives, which will no longer be necessary. A tunneller that can drive faster than highly pressurized magma, however, is. Carter sets out for the lake with the magma right behind him. Apparently, it didn't want to go up the tunnel they had already made, which is good news for Hood, as that would have meant a volcanic eruption in his backyard. Although he actually might have liked that.