Could you please tell me the meaning of "deep" in the following excerpt from Chapter Eight of The Great Gatsby?
Michaelis had seen this too but it hadn’t occurred to him that there was any special significance in it. He believed that Mrs. Wilson had been running away from her husband, rather than trying to stop any particular car.
“How could she of been like that?”
“She’s a deep one,” said Wilson, as if that answered the question. “Ah-h-h——”
In some of the old movies set in the 1930s shown on Turner Classics, the descriptive "deep" adjective is sometimes used by some of the gangster pr lower-class types, as in "He's a deep one, that one," implying that there is something mysterious about the person's activities, most likely some clandestine actions that are not legal or are immoral. This is what is meant by Wilson.
Poor, simple George Wilson is aware that his wife is going somewhere and meeting someone, but he does not know who the man is. Then, on the day that Tom comes through with Jordan Baker and Nick and buys gas, he sees Gatsby's splendid car. However, after the accident when the car is identified as belonging to Jay Gatsby, Wilson is perplexed since he has previously seen Tom Buchanan driving to New York in it. So, when Myrtle, whom he has locked up in the house in order to make her stay home, runs out as the car passes back through later in the day, he has assumed that Tom is driving, but learns that such is not the case. Therefore, when Michaelis asks Wilson how she could have done such a thing, Wilson replies, "She's a deep one---" implying that there is much about his wife's activities about which he has been unaware and much that he does not care to discuss.
That night as Wilson rocks back and forth, he tells Michaelis to look into a drawer that has an expensive leash and collar. He tells his neighbor that he has asked Mrytle about this leash after finding it, "She tried to tell me about it but I knew it was something funny." This statement and the experience of seeing someone else in the car besides Tom Buchanan lead Wilson to suspect that the owner of the yellow "death car" has tried to kill Mrytle. Thus, he finds Mrytle "a deep one" as she has engaged in surreptitious activities that have led to her murder and her "tragic achievement" has been complicated.
Standing behind him Michaelis saw with a shock that he was looking at the eyes of Doctor T.J. Eckleburg, which had just emerged pale and enormous from the dissolving night.
Departing on foot, Wilson has a way "of finding out" and seeing deeply into events, and by half past two that night, Wilson is in West Egg, heading for Gatsby's house.
George Wilson is about as pitiful a character as one could possibly find in literature; he is downtrodden, mentally and physically exhausted, a true symbol or metaphor for the blight outside of New York City that Fitzgerald refers to as the "valley of ashes". He knows, but tries to avoid thinking about his wife Myrtle's affair with Tom Buchanan, and after she dies he reverts to a state of denial, telling himself, and Michaelis that she was running to the car to talk to Gatsby. Michaelis is confused, as shown above when he states, "How could she of been like that?", and Wilson, clearly in shock, replied "She's a deep one," meaning the depth of her intentions, and feelings were complex, and that she clearly had some sort of important business with Gatsby propelling her emotionally towared the highway where she was hit. Long-suffering though he had been, Wilson still loved his wife, idolized her a bit, even, and the irony of his killing Gatsby to avenge his wife is that the both he and Gatsby had something central to their existence in common: they loved women who loved Tom Buchanan. True to what the reader has learned about the Buchanans' character, Tom and Daisy pack their suitcases and leave Nick Carraway to clean up the mess that has resulted from their actions, including but not limited to planning and carrying out the Gatsby's funeral.