Plot hole: In the end, we see that Francesca entered the bedroom, ruffed up the bed, and tied herself up before shooting Shale. However, if Katrina hadn't entered the bedroom moments after the fatal shooting, where is Francesca's alibi? If Katrina weren't there, Francesca would have been sat there for possibly hours. The police would reasonably guess she shot him and then tied herself up. How did Francesca know that Katrina was going to be there and at what time in order to testify to her innocence? (00:41:00)
Plot hole: Why on earth would a sleazeball like Adam Klaus be worried about news of a one-night stand being revealed? He'd welcome the publicity, if anything. Anyone threatening to go to the papers with news of a bit of rumpy-pumpy with him would be wasting their time.
Plot hole: How did the guy who stalked Emma Lazarus managed to get the box containing her head on the aeroplane without it being checked by airport security? As airline passengers are required to have their personal belongings on them scanned, this should have been detected by the airport security scanner and security staff would have detained the passenger or even arrested him before he had the chance to board the plane.
Plot hole: SPOILER ALERT Louise Bergman murders her father Marco, who is blind, by making a tape of the sound effects of a blazing fire along with her voice urging him to jump to safety out of his upper floor window. A man who has been blind for two years would have learned to rely on his other senses, and would immediately suspect something was wrong - he would feel no heat from the fire nor smell smoke.
The Sinner and the Sandman - S5-E2
Plot hole: Ian Avery-Cooper loses his lottery ticket which is immediately picked up and appropriated by Leonard Corbyn. However, Avery-Cooper immediately reports the loss to the shopkeeper who sold him the ticket. All lottery sales staff are trained in what to do under these circumstances, because it happens a lot - they cancel the lost ticket and issue a new one. Since Avery-Cooper used the same numbers every week this would not pose a problem, but even if he didn't the ticket would be recorded on the seller's computers and could be precisely reconstructed. This would be even easier since Avery-Cooper reports the loss within a minute of it happening and we see that he has the receipt for the sale in his hand. Corbyn's stolen ticket would be worthless and Avery-Cooper would be able to claim his rightful winnings. If nothing else Ian could have simply bought another ticket with the same numbers.
Plot hole: The entire plot hinges on Jonathan's solution of the murder of the first wife of Stephen Belkin. That work had the effect of exonerating Belkin. But, Jonathan's solution wouldn't exonerate Belkin in the slightest. It only explained how the murder was accomplished. It did not eliminate Belkin as a suspect. Even after Creek's solution, Belkin still had means, motive and opportunity. As the only surviving person in the locked room where the murder happened, Belkin would have remained the most obvious suspect. In fact, Creek's solution tended to show that only Belkin could have done it, precisely because the room was indeed locked - Creek never explained how a third person could have got in and set up the killing. but in the transmitted episode, it only occurs to Creek much later that, duh, of course Belkin did it.
Chosen answer: It was a bottle of turpentine.
Methylated spirit, always coloured purple.