_includes/latest-posts-grid.html

<div class="archive-wrap">
  <h3>Latest {{ page.categories | first | replace: '-',' ' | capitalize }}</h3>
  <ul class="th-grid">
  {% capture category_name %}{{ page.categories | first }}{% endcapture %}
  {% for post in site.categories.[category_name] limit:4 %}
    <li><a href="{{ site.url }}{{ post.url }}" title="{{ post.title }}"><img src="{{ site.url }}/images/{{ post.image.thumb }}" alt=""></a></li>
  {% endfor %}
  </ul>
</div><!-- /.archive-wrap -->