Quotation:

“‘If you think it necessary, by all means follow to see where he goes,–you are sure to meet somebody whom you will be able to send before you have gone very far.’ 

‘I suppose I shall.–You won’t mind being left alone?’ 

‘Why should I?–I’m not a child.’ 

[…]‘If I don’t make haste I shall lose him. I’ll do as you suggest–dispatch the first individual I come across to hold watch and ward with you.’

[…]I waved my hand to him. I watched him till he reached the end of the road. Turning, he waved his hand to me. Then he vanished, as Mr. Holt had done.

And I was alone.” (227-228) 

Comment:

This quote was a conversation between Marjorie Linden and Sydney Atherton when they were at the house Robert Holt initially broke into. Something I’ve noticed is that this story contains a lot of the elements of horror that have become cliche in modern monster stories. Most notably is the fact that ‘The Beetle’ is a mystical, shapeshifting entity that can control minds, but another common trope, which is represented in this quote, is a group of people who split up in the monster’s lair. I recognize that this is probably one of the first monster stories that contain this trope, but even still, it just seems unrealistic. Based on my limited knowledge of the time period, and knowing about Sydney’s initial reluctance to bring Marjorie along, it seems doubtful that he would leave her behind in a decrepit house that is likely the source of all the weird happenings that have been going on. 

Question:

Is there any logical explanation for where this trope came from? Has it ever been used in a way that stays true to the story it’s used in?