MongoDB query for related records

I have a blog application. I need to make a MongoDB query (SQL is fine, I'll translate it), to get a specific post in the blog, and the immediate posts made before and after that post.

For instance, given this list of posts:

12/01/13 - Foo
15/01/13 - Bar
17/01/13 - Baz
27/01/13 - Taz

How do I write a query so that I get one of these, i.g Bar, and the immediate siblings Foo and Baz?

I'd like to do this without making three different queries to the database, for performance reasons.

In my application I fetch a single post like this:

model.findOne({
    date: {
        $gte: new Date(2013, 0, 15),
        $lt: new Date(2013, 0, 15, 24)
    },
    slug: 'Bar'
}, function(result){
    return { entry: result };
});