Miss Emma gives another wonderful portrait of derangement, saying she must get the butler to tidy the dining room - tidy up the dead body, obviously - before dinner. Sapphire comments that motives are irrelevant, they're the setting for the time disturbance. She also comments that 'it' is getting closer, to which Steel replies that 'it' is fooling them by setting them puzzles, that they're innately bound to solve. So the sense of distraction is now clearly on the surface. Sapphire comments that they have a chance of winning though because 'it' has to deal with them both as Sapphire and Steel and Miles and Virginia. As they say this the dead body in front of them starts to change, ageing, going forwards in time - despite Steel trying to persuade Sapphire that ageing moves things backwards in time. Even the dining room becomes covering in dust and cobwebs as if it had just lain there for fifty years. It is interesting that while Steel picked up on the fact that 'it' is trying to trick them, he is so disorientated that Sapphire has to correct him on something which evidently seems totally simple to her, as it should to him.
They become aware that the gun is not in the same time frame as everything else in the room, it isn't marked or dusty, and Sapphire comments that it's going to be used again. Steel's normally calm demeanour slips markedly when he even has a note of panic in his voice as he tells Sapphire to get us back - now! Not only is he confusing times but is panicked by the fact that the dining room is apparently moving forward to 1980 around them.
The next 'trick' is the predictable one that the body vanishes, after the guests accuse Howard McDee of having a motive after blackmailing the victim. Steel is back on form enough to comment that he doesn't feel that is the solution to the problem. Sapphire's psychometry of the two murder weapons reveals that they were not used by a living soul to kill the victims. Steel makes the sense of deceit in the house explicit by verbalising it. Sapphire picks up the knife and goes to stab herself in the chest with it. Steel stops her doing this by pushing against the point of the blade with his hand.She then holds the gun to his forehead, says she is not sorry about this, squeezes the trigger, and finds he has removed the bullets. What Sapphire learns from this is the need to kill in the house. Sapphire also explicitly states the distraction motif: the 'power' resides in the house, and everything is irrelevant beside the central intention, to take time back to 1930 until time takes a different course. 'It' wants to rearrange history in 1930 so that the world ends. It focuses on the revivified George McDee. As Sapphire and Steel leave the library, we see the gun disappear.
I have ignored the Agatha Christie strand of this episode so far, keeping to my policy of trying to understand this assignment from Sapphire and Steel's point of view and treating everything else as part of the distraction, but at this point the Agatha Christie and Sapphire and Steel strands of the story merge. The guests have questioned why Lord Mulreen is so happy to have Steel investigate two apparent murders, and since he has told them and repeats that he is a detective of sorts, he - in true cosy detective story tradition - tells the assembled guests in the drawing room that he knows who will be murdered next. He advises Howard McDee not to take the next few hours too lightly. The dinner gong interrupts before any further questions can be asked, but clearly Steel has begun to suss what is happening.
During dinner - in which Sapphire has to tell Steel the social niceties - Emma Mulreen takes a trip to Lord Mulreen's office, transformed into George McDee's laboratory, to see him. It is clear that they are lovers. The time disturbances are felt as air and technology disturbances by Lord Mulreen's present-day secretary.
The next death is Howard McDee, just after he proposes an insulting toast to Mulreen and McDee, which is where the episode ends.
If this were purely a murder mystery, Sapphire and Steel would normally be considered the likely culprits - which indeed they are, and their presence questioned. However it is twisted in this story so that Steel is finally accepted as a fit person to investigate the murders. This is likely because of the seething tensions that are becoming apparent amongst the guests: they're really so wary/jealous, etc, of each other that they accept the initially unlikely outsider as the only neutral person to investigate.
There is, however a weakness to the Sapphire and Steel side of the story: 'Time takes over a house and its occupants with a view to causing the end of the world in 1930' is frankly rather a thin plot. Dramatically the parts of the story that I am treating as distractions from the main story that Sapphire and Steel are interested in, are essential to give interest to the plot. In fact it is the interaction of these two elements that make this assignment work so well.