Summer was the second story in the audio anthology, Circular Time, which comprised the ninety-first release in Big Finish's monthly range. It was written by Mike Maddox and featured Peter Davison as the Fifth Doctor and Sarah Sutton as Nyssa.
It dealt with the problems that arose from the Doctor carrying anachronistic money around in his pockets during the time that Sir Isaac Newton was trying to catch counterfeiters in late 17th century England.
The Doctor and Nyssa once again finds themselves imprisoned in the Tower of London. The Doctor laments that he got them into hot water by being absent-minded as he accidentally gave Nyssa coins from the wrong eras to pay their tavern bill with. Unfortunately, Sir Isaac Newton happened to present in disguise at the tavern, and he promptly arrested the duo for forgery.
Isaac Newton then personally visits them in the cell, telling them that usually he has forgers summarily executed, but since he finds the design of the coins strange and have noticed they are made from metals he does not recognise, so instead he wants answers from them. The Doctor tries to explain that they are travellers from far away and that is the reason for the strange coins, but Newton suspects there is more to it so he will keep them alive so they answer his questions.
Later that night, the Doctor and Nyssa are brought outside. Nyssa fears that it is an impending execution, but the Doctor assures her that such things are always done in public on Saturdays, so it must be something else. Instead they are placed before Newton again, who shows them that he has found the TARDIS and wishes to interrogate them about it alone. Having found that it is impossible to damage the TARDIS and having no other explanation for the design of the modern coins, and the fact that there is a genuine Roman coin and an even more futuristic triangle-shaped coin amongst them, Newton has deduced that the Doctor and Nyssa must be time travellers, as well as aliens, and the TARDIS their time machine. The Doctor and Nyssa tries to play dumb and explain that he is wrong and the TARDIS is merely a sedan chair, offering him to show him the inside in the hope they can distract him and escape, but Newton gets entirely caught up in his deductions and for a moment plays them no mind as he analyses the coins, predicting amongst other things the American War of Independence, World War I, the Irish War of Independence, the Moon landing, and the 22nd century Dalek invasion from them. Suddenly, snapping back to reality, Newton states that he believes the Doctor is travelling in time to gloat and views the past as "a series of trophies", and disgusted by this, he orders him and Nyssa imprisoned again.
Back in the cell the Doctor begins to worry about how just much the timeline has been polluted from all this. Borrowing Nyssa's ear-ring, he attempts to stage an escape by performing a parlour trick he learned from Harry Houdini, in which a piece of lead appears to turn into gold, to impress and bribe the jailer, but it falls flat, as the jailer prefers his steady job, and him and Nyssa are again brought before Newton. Learning about the trick the Doctor tried to pull, Newton is just as unimpressed as the jailer, stating that the Doctor is certainly no alchemist as he would know the secret of transmutation if he where. This prompts Nyssa to explain to Newton that turning base metals to gold is impossible, but on the quantum level certain elements can become something else, though not gold. Impressed by her knowledge, Newton asks the guards to step back so they can speak in private. Nyssa then goes on to explain who the Doctor is, telling about his status as outcast among his time travelling people, and how she met him, telling Newton that what he predicted might be true, but the Doctor was always there throughout history to help, while the Doctor tells Newton how much he respects him and of the impact he will leave on Earth's history.
Overloaded by this information, Newton starts groaning and twisting in response and the jailer notices that he is having one of his "funny turns" again, and advises the Doctor and Nyssa to let him cool down, but Newton angrily calls him a simpleton and orders him to leave, while demanding that the Doctor and Nyssa continue their tales about the future. The Doctor continues to extol Newton's legacy, telling him that continents on other planets and measurements of units will be named after him, and every child will learn of him in school, and this will go on for as long as England stands. Newton asks if this will be until the 22nd century invasion, which the Doctor confirms, telling him it was the best he could do. Newton says he believes they tell the truth, before having a seizure from the huge amount of information. Nyssa says it is their chance to escape and suggest they make a run for the TARDIS, but seeing Newton lying chocking on his own tongue, the Doctor refuses to leave him, saying that he will not allow a genius of Newton's calibre to die on his watch and tells Nyssa to run ahead.
The Doctor manages to calm Newton down from his seizure, and Newton laments how everyone is doomed to die and be forgotten. He asks the Doctor if they will ever meet again, to which the Doctor answers they will not. Satisfied with this, Newton tells him he is free to go and orders the guards to not let any harm come to him. The Doctor then rejoins Nyssa in the TARDIS, telling her that Newton will recover, and when he does he will be bored with the memory of them and move on to something new. Nyssa says she cannot understand why the Doctor would admire Newton so much, to which the Doctor responds that Newton's hidden talents greatly outweighs his less-than-ideal personality, to which Nyssa points out that the Doctor conjuring trick with the ear-ring was also a pretty impressive hidden talent. The Doctor then states he will now perform his next trick as he starts working the TARDIS controls.
- The Doctor - Peter Davison
- Nyssa - Sarah Sutton
- Guard - Jeremy James
- Molly - Sunny Ormonde
- Jailer - Trevor Littledale
- Sir Isaac Newton - David Warner
- Molly hints that another incarnation of the Doctor was imprisoned in the Tower of London a week before this story takes place.
- Isaac Newton says that he became an alchemist because he was given a book by an old man who is implied to be the First Doctor.
- In an attempt to appear like a magician the Doctor quotes "Who is the Doctor?"
- The Doctor refers to the Dalek Task Force.
- According to a 20 November 2006 blog post, Mike Maddox wrote this story based on an idea by Paul Cornell.
- The Doctor states that the Council of Nicaea was held in 354. In reality, it was held in 325, as was depicted in AUDIO: The Council of Nicaea.
- The American coin that is found on the Doctor is a 1978 Eisenhower dollar, a coin that was struck from 1971 to 1978 to commemorate both President Dwight D. Eisenhower and the moon landing.
- This story is set between Time-Flight and Arc of Infinity.
- The Doctor expresses interest in visiting the Council of Nicaea one day, which he would later do in the company of Peri Brown and Erimem. Newton also refers to Arius. (AUDIO: The Council of Nicaea)
- While imprisoned, the Doctor laments that he has not found the time to make a new sonic screwdriver since the original's destruction by the Terileptil leader in September 1666. (TV: The Visitation) The Seventh Doctor would eventually make a replacement. (AUDIO: The Dark Husband; TV: Doctor Who)
- The Sixth Doctor would later be imprisoned in the Tower of London on two separate occasions in 1590 and January 1555 (AUDIO: Point of Entry, AUDIO: The Marian Conspiracy), whereas the Eleventh Doctor would suffer the same fate in the 17th century but managed to escape with an "invisible sphere" (TV: The Impossible Astronaut). The Eleventh Doctor was eventually imprisoned again, as were the War Doctor and Tenth Doctor, in 1562. Ironically, their prison cell door was left unlocked. (TV: The Day of the Doctor)
- Isaac Newton mentions that his nose bled for three days after the apple fell on his head. The Fourth Doctor once claimed that he sat in Newton's tree dropping apples on his head and then explained gravity to him over dinner. (TV: The Pirate Planet)
- Isaac Newton predicts that the Earth will fall to invaders from another world in the 22nd century. Nyssa assures him that the Doctor will lead humanity in fighting back all the conquerors. (TV: The Dalek Invasion of Earth)
- The Tenth Doctor claimed that he had once taken Newton on a trip to Practas Seven, but he seemingly did not take the experience of travelling through time and space very well as he "sat in a corner and whimpered." (COMIC: Final Sacrifice)
- The Fifth Doctor uses a parlour trick taught to him by Houdini. He and Nyssa had previously met Harry Houdini in England in the 1920s, when he called the Doctor to help in the recovery of an Ovid sphere. (AUDIO: Smoke and Mirrors)
- Nyssa refers to the destruction of Traken. (TV: Logopolis)