There are often similarities in plot. Some people make it obvious and acknowledge the source of their inspiration. "West Side Story," for example, is Romeo and Juliet set in New York City in the 1950s. Some authors steal unintentionally when they should know better. The plot in Woody Allen's "Small Time Crooks" (2000) is nearly identical to the plot in the 1942 Edward G. Robinson comedy "Larceny, Inc.," although Allen has never acknowledged that and no one has sued.
Now let me discuss the law. The U.S. copyright laws are codified at vol. 17 of the United States Code (U.S.C.) §§ 101 et seq. In a copyright infringement case, the plaintiff must show: "(i) ownership of a valid copyright; and (ii) unauthorized copying of the copyrighted work.” Jorgensen v. Epic/Sony Records, 351 F.3d 46, 51 (2d Cir.2003). "To satisfy the second element of an infringement claim—the ‘unauthorized copying’ element—a plaintiff must show both that his work was actually copied and that the portion copied amounts to an improper or unlawful appropriation." Id.
Direct evidence of copying is seldom available, so the case law allows a plaintiff to establish copying circumstantially by demonstrating that the defendant accused of copying "had access to the copyrighted material, ... and that there are similarities between the two works that are probative of copying.” Id. However, a showing of similarities between the two works, coupled with access, does not necessarily prove copying because there would still be insufficient evidence of unlawful appropriation. A Slice of Pie Prods., LLC v. Wayans Bros. Entm't, 487 F. Supp. 2d 41, 47 (D. Conn. 2007).
To prove "unlawful appropriation" the plaintiff must show the existence of a “substantial similarity of protectible material in the two works,” with substantial similarity turning on “whether, in the eyes of the average lay observer, the [allegedly infringing work] [is] substantially similar to the protectible expression in the [allegedly infringed work].” Williams v. Crichton, 84 F.3d 581, 587 (2d Cir.1996). To determine substantial similarity, the Court or jury “examine[s] the similarities in such aspects as the total concept and feel, theme, characters, plot, sequence, pace, and setting.” Williams, 84 F.3d at 588.
What a copyright owner can't sue you for copying are such things as “scenes a faire, sequences of events that ‘necessarily result from the choice of a setting or situation," ‘stock’ themes commonly linked to a particular genre, and ideas, because “a copyright does not protect an idea, but only the expression of an idea,” A Slice of Pie Prods., 487 F. Supp. at 47 (citations omitted).
In sum: If you read anything that is like the work you are writing, be careful. You can adopt the idea (e.g. war is hell, power corrupts, etc.) or the stock theme (e.g. lovers who are forbidden to each other by their families) If you get sued, a legitimate defense is that you never heard of the plaintiff's work.
With that in mind, recognize that George Harrison's song "My Sweet Lord" was found to be substantially similar to the 1962 Chiffon's hit, "He's So Fine," and Harrison admitted that he was familiar with the song.
The Beach Boys' brilliant composer, Brian Wilson, however, now admits that "Surfin' USA" was written as an homage to Chuck Berry. "I just took 'Sweet Little Sixteen' and rewrote it into something of our own," he told the Los Angeles Times. Wilson's problem is that his version is substantially similar to "Sweet Little Sixteen," so much so that Wilson often slips in Berry's lyrics when singing "Surfin' USA" in concert. Id.
If you try to write something "in the style" of another author, be very very careful. It is a jury that decides whether your work is substantially similar to the plaintiff's work, and sometimes their decision may not exactly be "substantially similar" to the boundaries drawn in copyright law. I personally didn't think that "Blurred Lines" was substantially similar to Marvin Gaye's "Got to Give it Up," aside from the party-type atmosphere, which shouldn't be a protected aspect of the song. But a jury thought otherwise. Fortunately, a jury verdict is not precedential or controlling beyond that case.