Once you click on (+) and then on the "Read Later" link; you can click on "Offline Links" to get a list of all pages saved for reading later. These are stored locally and accessible even without an internet connection.

The "Offline Links" is available only after Tranquility Reader has processed a page. So, you will first have process some page first before you can access "Offline Links" saved in earlier sessions. This is a limitation of the current design. In future releases, I will try to add more user friendly ways to access the offline content without needing to run Tranquility on some page first.