"The British crown has been plagued by scandal."
Let's analyze the sentence, then pinpoint the rhetorical devices, also recognized as literary devices, that are operating in it.
Starting with the latter half, "has been plagued by scandal," we are faced with a figure of speech. Figures of speech are phrases that have figurative, non-literal meanings that supersede the literal meaning of the words. Let's take a more obvious example to clarify this.
If I say a dress is "the bees knees," as someone might have done in 1920, you know that I do not mean the dress is somehow the knees removed from a giant bee or a bunch of bees. The literal meaning here makes no sense. Yet the figurative, non-literal meaning does make sense to anyone who knows this figure of speech. For some reason clear only to flappers from the 1920s, "bees knees" figuratively means really, really good. Thus the dress that is the bees knees is a really, really good dress, probably beaded with fringe.
This kind of figure of speech (and there are many kinds of figures of speech) is called an idiom: idioms have literal meanings that are senseless in context while the non-literal meaning, known within the culture, carries the true meaning.
The figure of speech idiom in the phrase we are considering is "plagued by scandal." Since this is figurative, not literal in meaning, we know there are no locusts, grasshoppers, or Black Plagues involved in the scandals. What culturally agreed upon meaning is there then? The idiomatic formula to plague somebody with/by something means to overwhelm and annoy somebody with/by something.
In this idiom, then to plague somebody (the British crown) with/by something (scandal), means to annoy and overwhelm them with scandal. So the paraphrase of this rhetorical and literary device "has been plagued with scandal" is: has been overwhelmingly annoyed by repeated scandals.
Looking now at the first half of the sentence, "The British crown," we are faced with another figure of speech. This one is a rhetorical device that is used to quite often in daily British language but rather less so in American daily language. This rhetorical device substitutes a larger concept with a shorter word or phrase: a general concept is replaced by a representative related word or phrase. This rhetorical device is called a metonymy [there are two forms of metonymy: metonymy (e.g., U.S. Government = White House) and synecdoche (e.g., sailors = hands)].
The rhetorical figure of speech called metonymy we are considering is "British crown." Again, this has a literal meaning that is senseless in context. Yet it has a non-literal, figurative meaning that communicates an understood larger concept.
Specifically, we all know that a crown in of itself cannot rightly be said to be overwhelmed or annoyed by anything. Thus "crown" substitutes for a larger concept that is figuratively understood through the metonymy of "crown." The larger, general concept is the crowned ruler of Great Britain; today this is Queen Elizabeth II and may conceivably include the Crown Prince, Charles, Prince of Wales.
Thus the two rhetorical devices, also called literary devices, in this sentence are, in order from the beginning, the metonymy "British crown" and the idiom "plagued with scandal." Recall again that both are figures of speech in which the literal meanings are senseless in their context while their figurative non-literal meanings carry all the culturally defined and agreed upon meaning.