Season 10 Episode 02

Alphy and Meg Grey go on their first proper date: they swap books and arrange a picnic. They kiss in Alphy's open car outside the vicarage and are interrupted by the bishop, who turns out to be Meg's father. He tells Alphy he is aware of his reputation while Meg waits, and Mrs Chapman and Leonard listen from the house.

The case begins with a student, Christina Parsons, found dead beside a crashed scooter near Newnham College. The scooter key is missing and there are no grass marks or skid marks on the body, which suggests the crash was staged. Her bag holds a ring made from an American dollar coin and a copy of Sartre. The scooter is registered to Peter Grayson, a college janitor, who says he lent it to her, and the Sartre was his too. He is a Mod, and she became interested in him and in the subculture when she first saw him out of his work clothes. He has a previous arrest for brawling, so Geordie treats him as a suspect. The Newnham porter saw Christina arrive at the laboratory before nine and leave in helmet and parka a little after ten.

Christina was a researcher for Professor Clarence Aldo. The detectives first meet Aldo interrupting a lecture by Professor Madhu Joshi to demand that she retract a genetics paper she has just published, and Joshi throws a glass of water over him. Both want credit for new work and a faculty chair is coming up. Aldo says she published too early and she says he sat on his results. Terry Betts, a scholarship student who works for Joshi and had collaborated with Christina, says he saw her leave the lab and claims she had been fighting with Grayson, and describes himself as an outsider whom Christina defended from bullying and who helped her with her coursework.

Christina died of head trauma from what looks like a flat surface, although she was wearing a helmet when she left, and there is a regular row of puncture wounds across her back. Alphy notices that Aldo's papers are about coins and works out that Aldo made and gave Christina the coin ring, so they were having an affair. Grayson's scooter keys are then found in his bag, but he was in the library at the time, where the librarian confirms he had been reading at night, so the keys were planted. A blood spot is found outside the laboratory window, and Alphy finds a broken piece of a DNA model with spikes matching the punctures on her back, with dried blood on it. She was killed in the laboratory, and someone left in her parka and helmet for the porter's benefit, then took the body out through the window, staged the crash and planted the keys. Alphy finds that Aldo's figures in Christina's notebooks match Joshi's published paper exactly, meaning Joshi used Aldo's research. Joshi, confronted, says she went back to the laboratory in her gown with a bottle of wine to try to replicate Aldo's results herself. Her accusation that Alphy had betrayed his Indian identity turns out to have been about herself, since she regrets having set her own background aside to fit in. She fails to replicate the results and at the police station realises why, which is that Aldo faked them, and that is why he never published.

The published recap's account of the killing is that the handwriting beside Aldo's results in Christina's notebooks is Terry Betts's, since he helped her with her work and used the access to steal Aldo's results for Joshi. When Joshi published, Christina understood what he had done and confronted him in the laboratory, threatening to tell his parents. Terry, desperate to keep his place and to satisfy parents who had worked to send him to college, pushed her. She fell into the DNA model and then he threw her again and she struck her head on the table and died, and he staged the crash and planted the keys to protect himself.

Two supporting threads run across the case. Larry Peters keeps proposing to Miss Scott and she keeps refusing, because marriage would mean leaving her job at the station; he can only see the wedding and she cannot make him hear that she does not want her future mapped out for her. Cathy's input is overlooked again at Swinnerton's, where a man chooses the women's clothing range, and Geordie makes more of an effort to listen to her, then comes home to find his son David in a dress, dancing to pop music, and orders him to take it off. He tries to make sense of it by asking Leonard about his sexuality, which leaves him no further forward. Alphy, rattled by Joshi's charge, lashes out at Meg when she comes to apologise for not telling him who her father was, accusing her of using him to rebel against the bishop. He works through the papers with Leonard, who is drinking more heavily in Daniel's absence, tells Leonard he already regrets it, and later takes the promised picnic to the library to apologise. He asks her to dinner at the vicarage, and says he will cook.

The episode is a laboratory murder built out of an academic quarrel that turns out to be a plagiarism case, and the answer is in a young man's handwriting in someone else's notebook. The DNA model is the best physical clue of the series, since a broken stand with blood on the spikes is what proves the death happened indoors and the crash was staged with a parka and a helmet. Joshi failing to replicate Aldo's results at the station is the neatest way the episode could have said that the science was invented.