Sophie Stark was Juliet Ashton's childhood friend in The Guernsey Literary and Potato Peel Pie Society, and Sophie had an older brother, Sidney, who Juliet knew but was not really friends with until he became her editor years later. Both of the Starks are ideal friends and correspondents to Juliet in Mary Ann Shaffer's book.
Sophie is a good friend for Juliet (aka writer Izzy Bickerstaff), though we never read an actual letter she writes; we only hear what she has written when Juliet responds to Sophie's letters. Sophie is the person with whom Juliet shares her personal life. As she talks about the people she meets in Guernsey as well as from her "London life," Juliet reveals her feelings, especially about the men she is thinking about . Sophie is a good friend and asks the hard questions (but in the nicest possible way, of course). In other words, she wants the details.
In response to one of Sophie's letters, Juliet writes this:
Your questions regarding that gentleman are very delicate, very subtle, very much like being smacked in the head with a mallet. Am I in love with him? What kind of a question is that? It's a tuba among the flutes, and I expect better of you. The first rule of snooping is to come at it sideways....
Sophie is a settled woman who serves as a voice of reason for Juliet, whose emotional attachments are undergoing some rapid and surprising changes.
Sidney Stark, on the other hand, is the person with whom Juliet corresponds about her writing life. For example, here is most of one of her early letters to him.
Now for my grim news. You asked me how work on my new book is progressing. Sidney, it isn't.
English Foibles seemed so promising at first. After all, one should be able to write reams about the Society to Protest the Glorification of the English Bunny. I unearthed a photograph of the Vermin Exterminators' Trade Union, marching down an Oxford street with placards screaming "Down with Beatrix Potter!" But what is there to write about after a caption? Nothing, that's what.
I no longer want to write this book—my head and my heart just aren't in it. Dear as Izzy Bickerstaff is—and was—to me, I don't want to write anything else under that name. I don't want to be considered a light-hearted journalist anymore. I do acknowledge that making readers laugh—or at least chuckle—during the war was no mean feat, but I don't want to do it anymore. I can't seem to dredge up any sense of proportion or balance these days, and God knows one cannot write humor without them.
She talks with Sidney about the people and places she is experiencing in Guernsey both as a friend and as an editor in the context of a writer talking to an editor about a story. It is true that they are friends, as well, but the nature of their correspondence is still centered around a potential story. He is the one who cuts through her random observations to help her see the truth about what kind of story, or actually whose story, she should be telling.
Each of the Stark siblings allows Juliet to express herself and glean useful advice, one on a purely personal level and the other on a bit more professional plane. Without both of them, the readers would only know one side of Juliet's life.