I've read this book a few times and I'll probably revisit it again; it's a favorite.
"Last Summer" is the story of three teenage friends - Sandy, David, and Peter (the narrator) - who spend summer vacation on an island. Regularly slipping away from their parents, they create a little mischief throughout the summer - stealing beer from their homes, drinking, going topless (Sandy), bogusly filling-out a dating questionaire, etc. Their little circle is tight, until they "adopt" a sensitive and awkward freckle-faced girl named Rhoda.
The symbolism in the book is easy to see - just the way I like it. (What's the point of symbolism if nobody understands it?) The novel is divided into two parts: the first half is called "The Gull" and the second half is called "Rhoda." That makes it all the easier to understand the symbolism - the seagull and Rhoda are the same; both are wounded animals, both are adopted by the threesome, nurtured back to strength, and then cruelly betrayed, destroyed, and abandoned. Read the book with this in mind, and you'll see what I mean.
This novel is very real. Kids can be cruel, especially when trying to conform to the attitudes of their friends. This is the story of a "last summer" of innocemce - if not for all four characters, then at least for Rhoda.
There was a sequel called "Come Winter" which I borrowed from the library once and never finished. Maybe I'll have to give that one another try. In any case, I think I'll read "Last Summer" again. You should read it, too. (And check out the film starring a young Barbara Hershey, a young Bruce Davison, and a pre-Waltons Richard Thomas.)