This is something that I wished I’d thought of a long time ago – show other posts in the same series using not a plugin but custom fields. All you’ve got to do for this trick to work is create a custom field ‘Series’ with a link to each other post in the series. Each post must be a seperate custom field. Then, use the code below to display all the other posts in the same series!

<?php $series= get_post_meta($post->ID, 'Series', false); ?>
<h3>Also in this series:</h3>
<ul>
<?php foreach($series as $series-post) {
echo '<li>'.$series-post.'</li>';
} ?>
</ul>