There's no other way to describe this story than "Isaac Newton gets alien coins and goes mental." You'd think that'd be a really bad story, but it kind of works. Most of the story revolves around him questioning the ethics and science behind time travel and the future, and it makes an interesting character piece.

The Doctor and Nyssa are arrested for forgery, and one mistake causes Newton to break down, predicting the entirety of Earth's future. This is a very mature, powerful story discussing the importance of the Ripple Effect, the explanation of which is discussed in this story by Newton. The Doctor has to face the consequences of what his meddling actually does - something set up to be a negative thing from the previous episode (Spring), whilst Nyssa is just... there. There's a little moment where someone talks to Nyssa about how time travel has changed her outlook, but part of her still believes inside that it's not real, but beyond that, this story really pushes the Doctor and Nyssa out of the way.

Um, I guess the enemy of this story is time? It's a very unique story, so there's no real monster of sorts, just a discussion about what the Doctor really does. It's a welcome change, but there's a reason this isn't four parts.

The Doctor must be bored of getting locked up in the Tower of London every week. I think 17th Century London is a great time period to explore, but nothing really happens with it, and the majority of the story is spent in a dank prison cell. Meh.

David Warner steals the show like always - he's involved with a variety of Doctor Who stuff - Unbound, Cold War, and now this. The character of Isaac Newton is engaging and innovative, and his performance is superb. I think, for many, this is what makes the story a classic, but I don't think that this is enough to sell the story. It's a bit far-fetched how easily he works out that they're time travellers. It's nice to see someone actually thinking for once, but "this coin is a triangle and therefore the Daleks invade the 22nd Century" is really bizarre. Why is there even currency during the Dalek Occupation? The other side characters are a bit sidelined - this is really a back-and-forth between Newton and the Doctor.

The music's alright, nothing too interesting, unfortunately.

Favourite Line: "I’m so glad you didn’t pay by debit card."

It's a cool idea, but way overrated. I'm honestly left so confused by what the hell happened. It's a story that doesn't have enough substance for two parts, but is way too rushed for one. The performances and ideas, however, are excellent, I love the dialogue, and I did enjoy it overall - but it's just way too confusing to get a hold of.