TOC shows only a single level-one head

[TomSwan]

I get a toc but it only shows H1 level heads, nothing more.

I installed nokogiri, and in _config.yml I put;

gems: [nokogiri]

then in head.html:

<link rel="stylesheet" href="{{ "/css/toc.css" | prepend: site.baseurl }}">

and in default.html change {{ content }} to:

{{ content | toc_generate }}

I copy toc.css to css folder, and tocGenerator.rb to _plugins.

That, I think, are all the steps in the README instructions. The toc box
appears but only a single Level H1 head is shown. Am I missing something?