get_post_ancestors with wp_query

Hi.

I’m building a site using WordPress as a CMS and which uses pages almost exclusively to organise content.

I’m trying to find a way of creating a navigation menu which lists all the child and grandchild pages of top level pages, so the menu stays the same as you browse child and grandchild pages. There’s a couple of solutions around which work perfectly when using wp_list_pages and get_post_ancestors but I would like to include text excerpts from the pages too, and for that I think I need to use a wp_query.

I wonder if someone can help?

The wp_list_pages version of the code is as follows:

<?php
global $wp_query;
$post = $wp_query->post;
$ancestors = get_post_ancestors($post);
if( empty($post->post_parent) ) {
    $parent = $post->ID;
} else {
    $parent = end($ancestors);
}
if(wp_list_pages("title_li=&child_of=$parent&echo=0&sort_column=menu_order" )) { ?>

<h3><?php $page = get_post($parent);
echo $page->post_title; ?></h3>

<ul id="secondary-nav">
    <?php wp_list_pages("title_li=&child_of=$parent" ); ?>
</ul><!-- #secondary-nav -->

<?php } ?>

(code adapted from this post)

Essentially I’m trying (and failing) to replace the second wp_list_pages bit with code which enables me to include text excerpts as well as just page titles and permalinks.

Any help much appreciated!