The Situation:
By this point, Mr. Boddy has been killed again and there has been a small panic in the hallway before they bring all the bodies into the study for safekeeping. After a short discussion that reveals that weapons are all over the place, Wadsworth suggests that all the weapons be locked up in the cabinet. As they open the front door to throw away the weapon key, the Stranded Motorist appears looking to use the phone. After some discussion, the group invites him inside to use the phone in the lounge. They key then gets thrown away.
The Murder:
This is where we see the first concrete evidence of a murder plot. Recognizing the motorist, Col. Mustard then interrogates Wadsworth to see if there is anyone else in the house. Under the pretense of verifying that the house is empty, Mustard hatches the plan to split up and search the house in pairs. Clearly, Mustard has already made the decision to kill of the person informing on him.
There hand of fate is firmly on the scale against the Motorist at this point. By blind luck of the draw, Mustard, paired with Scarlett, draw the stick that places them on the main level with the motorist. We see the various pairs searching but the Mustard pair is the only one that matters. First they check the billiard room. Then they check the hall closet. Aggressively. When they get to the piano room(?) Mustard leaves Scarlett to go "search the kitchen". Now that they are separated, Mustard goes to the study and burns the evidence, retrieves the wrench and kills the Motorist.The next time we see Scarlett, she and Mustard have reunited in the Conservatory where Mustard "finds" the secret passage to the lounge. He breaks character and volunteers to go first, knowing that there is no danger because he already killed the Motorist using the same passage. At no other point does Mustard display the willingness to risk himself into the unknown. The screaming of Ms. Scarlett brings the others back to the main level, Wadsworth tries to break down the door, Yvette ends up shooting the lock and the chandelier falls, shatters and the Off Duty Policeman arrives. The secret passage is revealed to all.
The logistics of the murder make some sense I suppose. Col. Mustard splitting from Scarlett should have been a huge red flag but then again, White and Wadsworth separated as well and didn't think it was odd so who knows. The only real question is whether or not Mustard had enough time to do all the things he did. When he claimed to go to the kitchen he actually returned to the study, gathered up the evidence, threw it in the fire, unlocked the cabinet, got a weapon, ran to the Conservatory to use the secret passage, enter the lounge, kill the Motorist, return to the conservatory and then go back down the hall to where Ms. Scarlett is, in such a way that looks convincingly like he is returning from the kitchen. During this whole time frame, Ms. Scarlett is . . . . . . looking behind a curtain. I don't think there is any way Mustard could have done all that in the appropriate time frame but a little leeway should be given I suppose for movie magic.
Wadsworth on the other hand has completely lost control of his master plan. He invited the motorist to the house but after that he was out of the picture entirely. Not only did the drawing of straws put him upstairs with another known killer (Ms. White), he himself has led the charge to lock up all the weapons in the cabinet. Maybe Wadsworth could have guessed that the former soldier in Col. Mustard would try and kill the Motorist but that doesn't explain why Wadsworth would actively make it harder to do so.
And finally we come to the Motorist himself. What exactly was the plan? Like the fake Mr. Boddy, the motorist was invited by Wadsworth and given the role of the Stranded Motorist to play. We know this is so because if he was in fact a stranded motorist, there would have been no reason to pretend he didn't recognize anyone who answered the door. He would have just asked his co-conspirator Wadsworth to use the phone. So we have to assume that everything that the Motorist did was under order from Wadsworth, which begs the question as to what he was doing. Why on earth did the Motorist call anybody and why was he still performing the confused stranger surrounded by weirdos routine on the phone? Wadsworth went to great lengths to make sure all his accomplices and victims were gathered under one roof. Why would Wadsworth have instructed the Motorist to involve an outsider in the operation? It makes no sense. As we shall see again, the only reason the Motorist needed to make a call was because the script needed to distract him from his own impending murder. There is no in-movie logic that explains it otherwise. The only guess I could come up with is that the Motorist came to the house as Wadsworth instructed but then quickly sussed out the fact that something was off. But if that was the case, he would have been calling for help to arrive quickly, not meandering around the fact that his old boss was at a weird dinner party. The Motorist, Like Mr. Boddy and later the Policeman, is caught in the loop of acting in such a way that their actions only make sense if they are in fact their characters and not accomplices putting on a show. Which is of course impossible. There was also no reason to actually wreck his car if Wadsworth simply invited him to the house. He could have pretended to be a Stranded Motorist without actually leaving a bunch of evidence on the road.
Aside from all that, the actual footage in the movie fails to address one last fact vital to this murder. How exactly did Col. Mustard know about the secret passage? We know that's how he killed the Motorist because we actually saw it in the third ending but we aren't given that bit of information. There are only two scenarios given that explains how people know about the passage. The first is from Wadsworth who says that the house is a friends and that he's known all along. There's no reason why Wadsworth would have told Col. Mustard about the passage. The second way is through Yvette. In the first ending Wadsworth explains that Yvette told Scarlett about the passage so she could kill people. That doesn't begin to answer why Yvette would know about the passage at all, she wasn't a full time maid at the house or anything, and it also doesn't explain why Yvette would tell Col. Mustard. Yvette is getting paid to inform on Col. Mustard, why would she help him destroy the evidence of their affair? That would upset both Mr. Boddy and Ms. Scarlett as they both have dirt on Mustard. The only reason I could think of is that Yvette wanted the photos destroyed as well because she was in them but Wadsworth made it seem like Yvette did that sort of thing regularly for Ms. Scarlett. Destroying one set of photos probably wouldn't matter much in the final analysis.
Conclusion:
The logistics of the murder work fine but the timing in its execution are suspect, as are the behaviors of the Stranded Motorist and Wadsworth. By this point, the movie is relying on the novelty of the multiple endings plus the manic energy of Wadsworth's explanations to conceal the nonsensical parts of the plot that become apparent on repeat viewings. And for the most part its effective. By the time you get to the final ending you kind of confuse whats happened in which ending and whats actually real. It makes the proposed solution seem logical.
Up Next:
Murder #5, the Off-Duty Policeman. One of the funnier scenes in the movie and again, some of its least logical.
Wadsworth: 0 murders
Peacock: 1 murder
Green: 0 murders
White: 0 murders
Mustard: 1 murders
Scarlett: 0 murders
Plum: 1 murder
Mr. Boddy: dead
The Cook: dead
Yvette: alive
Stranded Motorist: dead
Off Duty Cop: investigating the Stranded Motorist's car
Singing Telegram Girl: not arrived