The synopsis should not "tease." It should tell the whole story: beginning, middle, and end. It should tell us who the "major" characters are and what they do. Skip minor details or subplots. If the subplot is major/parallel with the main plot, mention it, too, but don't let it overwhelm your main story. You may quote a few passages from the book, but don't overdo it. Some people debate whether one should write the synopsis in a similar style of the novel itself. Do what is best for you. Be specific (not vague) while skimming the details. A good way to do it is write the whole story first (don't worry about page count), details and all, then trim out the fat, the extraneous adverbs and adjectives, and minor plot/characters. Trim and trim until you're down to 3-5 pages and the story is still coherent. You'd be amazed how much can be said, specifically, without all the details.