In the console room of the TARDIS, the Doctor becomes very distressed at the readings on the instrament panels. When Sarah queries his strange behaviour, he replies that the relative dimentional computer has malfunctioned. In short, the steering's gone haywire. Examining the chronometric astrometer, the Doctor estimates that Earth Time will run out soon. The TARDIS stops, in the grip of some unknown force 4,500 million years into Earth's past, the very beginnnings of the planet. The Doctor realises this, and he and Sarah board a two person capsule to venture outside to observe it.

They make their way out into space, observing the unformed Earth. At this stage it is much bigger than the Earth of Sarah's day, an enormous mass of pulsing, burning gases. After observing this, the Doctor and Sarah pilot the capsule back to the TARDIS.

Back in the console room, Sarah comments on the frightening nature of the Earth's beginnings. Using cosmo-retrozine, the Doctor frees the TARDIS from the force gripping it, travelling along the progression trail of the developing Earth.

The TARDIS travels a few million years forward when it is caught in the pull of a huge force again. The Doctor and Sarah board the capsule to see how the Earth has progressed in those few million years.

Once outside the TARDIS, Sarah notes that the Earth has gotten smaller. The Doctor notes that it is closer to the size of Sarah's Earth, due to the erosion effect of sun action. The Earth has also begun to solidify, bringing order to the planet.

Hissing noises and thunder interrupt their conversation, but the Doctor dismisses it as lightning, noting that the first crust is forming on the Earth. A deep, echoing voice rises up, demanding to know the reason for the Doctor and Sarah's intursion. The Doctor replies that they are travellers. The voice reveals itself to be that of "Lord Megron, High Lord of Chaos, Chief of the Carions, Lords of Chaos." The Doctor mentions that he is a Time Lord, to which Megron replies that the Carions and the Time Lords have been enemies down through the ages. He states that he has taken over the firey Earth in order to perserve tis disorder for all time. To this the Doctor replies that order is already progressing from this tumult. This angers Megron, wishing that they be punished. The Doctor dismisses this lightly and Megron fires a thunderbolt. Tha capsule is unharmed. It returns to the TARDIS.

The TARDIS takes off, travelling along Earth's progession. Some million years later, the TARDIS slows and stops at another stage in Earth's development.

The Doctor and Sarah again enter the capsule and head out into space. They have different reactions to the scene before them. The Earth is being ripped apart by volcanoes. Sarah thinks its horrible, but the Doctor says it's marvelous.

By means of the compressive telesight, which allows events of millions of years to be viewed in minutes, they witness the volcanoes boiling the rock into cream, shuffling materials, moulding the Earth. Sarah feels sick and frightened, but the Doctor dismisses this and marvels at the forming Earth. Tidal wave covers contenents and mountains rise from the Earth. The Doctor comments that order is forming. To this Megron appears and dismisses it, referencing the vocanoes and lack of breatheable air. The Doctor taunts him with the word "order." Megron is enraged and parades his title "High Lord of Chaos." The Doctor points out that the Earth is generating its own gases, including a bit of oxygen. Megron denies this. The Doctor points out that the forming granite crust. Progess. Order. The Doctor states that life will take over the planet, which upsets Megron greatly.

The Doctor and Sarah move back into the TARDIS and continue on Earth's progression.

The TARDIS lands. The doors open, allowing an inrush of sweet air. The Doctor and Sarah step onto the Earth.