This novel of suspense is a little grittier than its predecessors (The Embroidered Sunset introduced Dr. Adnan; A Cluster of Separate Sparks introduced the fictional island of Dendros and its unique fictional species of butterflies). Though most people on Dendros are still nice, Mrs. Meiklejohn is holding a grudge, Kerry Farrell is a transsexual, Dikran is a terrorist, Dr. Adnan is beginning to recover from Lucy and feel attracted to young Priscilla Meiklejohn, and "Mike" ("my given name is suitable only for tombstones") is just beginning to notice these things and connect them to her sheltered schoolgirl life. There's even a scene where, although we're spared the details, we're explicitly told that Dikran and Julia are in bed (well, they're there on honeymoon after all).
The ending can be called happy, although to preserve suspense I won't say who's murdered and who's injured but going to live happily ever after. The baddies are identified and punish themselves, and Dr. Adnan gets the happy ending some readers wanted him to have in "Sunset."