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One single coin can set off a fascinating sequence of events... if you're a Time Lord.
The Fourth Doctor is sitting outside a shopping centre. He is preparing to toss a coin when he is interrupted by a security guard, Dennis Brown. While they talk, with Brown instantly taking the Doctor for a lunatic, a cyclist some distance away is covered in paint as a workman knocks a pot of premium gloss over her.
Now, back at the original starting point, the Doctor rolls the coin towards a pigeon, undisturbed by Dennis. It flies off and a teenager comes along and, seeing the coin, stoops to pick it up. A businessman, engrossed in his newspaper, promptly trips over him. The coin lands in the fold of the newspaper and when the businessman picks it up, flies out and jams in the spokes of a woman's bicycle. This time, the paint spills harmlessly.
The Doctor begins to untie one of three knots in his scarf. Meanwhile, the cyclists dismounts and moves to pick up the pound which has settled in a delivery bay. As she does so, a "Sam's Sandwiches" van sounds its horn, startling her. She moves, signals her apologies and cycles on. The coin is under near-side back tyre. Sam steps out and fetches sandwiches from the back.
Across the road, Emma tries to avoid staring at him. He greets her as he passes into an office building, prompting her to blush and drop the pound coin she was putting into a parking meter. The coin rolls into the road where a passing group of children inadvertently kick it further along. Emma does not see this and believes it is under the van and so stoops to look. Sam comes back and greet her again causing further blushes. The two laugh and the circumstances and the Doctor unties the second knot in his scarf.
Emma's coin rolls into a builder's trench, lands on a workman's spade and is batted into a long plastic pipe being hauled on a winch up the wall of the shopping centre by a second builder. The pipe is not straight, meaning that the coin rolls towards the end closest to the Doctor, gaining momentum.
The Doctor stands to watch proceedings and prepares to untie the third knot, but expresses displeasure when he sees Dennis approach to collect litter and stop to talk to the builder. The conservation does not end amicably, as the Doctor can tell, with the workman turning away to resume his task. The pound falls from the pipe into a cement mixer. The Doctor releases the knot and, looking to the sky, asks if he is being tested.
Again, the Doctor returns to the original moment. He triggers events once more with his coin and counts off each as they happen. The pigeon flies off, the teenager collides with the businessman, the cyclist allows Sam to park and Emma and Sam arrange a date in the local Italian restaurant. As Sam drives off, Emma finds the Doctor's coin. The Doctor again unties the second knot.
Emma's coin goes from the spade to the pipe. This time, Dennis does not appear so the worker is not interrupted. The pipe is winched higher, so the coin descends in a greater arc. It lands in a market stall awning and bounces into the sweet stall opposite, landing in the cash register. Startled, the stall owner knocks a table and a packet of sweets fall into a passing woman's handbag. The Doctor deftly lifts the sweets from the bag as the woman's handbag, remarking that they were "bought and paid for". He unties the third knot. Dennis approaches the Doctor and enquires is he well. The Doctor tells him that the coins were fixed in space-time and tells Dennis the fact he is not is highly unusual.
Sarah Jane approaches and, noting the security guard, asks the Doctor if he is in trouble. The Doctor replies that he was telling Dennis how amazing he is, being "almost immune to time". As they walk away together, Sarah asks if he was bored. The Doctor tells her he kept himself amused and offers her a jelly baby.
- The Doctor imitates shooting a pigeon before rolling a pound coin at it.
- According to the Doctor, aside from Time Lords, there are only fifteen known entities in the universe who are not fixed in time.
- Chain Reaction does not feature Sarah Jane in her usual companion role. She does not appear until the very end, having been about her own business.
- The Fourth Doctor again displays an affinity for jelly babies. (TV: Robot)
- The notion of individuals being fixed in time is explored. (TV: Father's Day)