The rather jaded Ms. Baxter substitutes for Milo's science class, finding no enjoyment in her job until her encounter with Murphy's Law. Meanwhile, Dakota and Cavendish find themselves in the science class's closet when they're supposed to protect a pistachio plant in the school yard.
Ms. Murawski's class is taken over by Ms. Baxter, a disillusioned substitute who finds no fulfillment in her job as she has no way of knowing if her students ever learn anything from her. Milo soon volunteers to help out, only for a simple science experiment to turn hazardous due to Murphy's Law. Meanwhile, Balthazar Cavendish and Vinnie Dakota end up in the classroom closet on their way to bring pistachio plant fertilizer from the future to a sapling. However, their Quantum Localizer loses power, and they are forced to plug it in to charge; Ms. Baxter then ends up getting a hold of it and being transported briefly into space.
After Milo takes over the class, an accident with a spilled chemical and the fertilizer - which Milo grabs thinking it's chemical absorbent - results in the creation of a sentient blob that attacks the students, Ms. Baxter, and the two time travelers. However, Ms. Baxter's lesson on the phases of matter inspires Milo, who works together with his friends to turn most of the gelatinous being into a harmless solid. Dakota and Cavendish are able to save a pistachio sapling from Diogee only for Cavendish to step on it, while Ms. Baxter is thrilled that she actually managed to teach something to her class. However, a sole surviving portion of the blob finds and revitalizes the crushed pistachio seedling, with its leaves turning red and emitting an ominous glow.
For a full transcript of "The Substitute", click here.