Here it is, a free download link for Avatar: The Rift Part One. The full comic is available below for download in a .ZIP file format. After extraction, you will recieve all the pages in high quality pictures, organized in a folder.
If you would like to read an 8-page preview before you download, check this page. Also, I highly recommend purchasing a copy of the book as well. It's always beneficial to support the publishers.
Summary: Avatar Aang asks his friends to help him honor Yangchen’s Festival—one of the highest Air Nomad holidays, which hasn’t been celebrated in over one hundred years.But cryptic visits from the spirit of Avatar Yangchen herself lead Aang to discover a jointly owned Fire Nation and Earth Kingdom refinery—operating on land sacred to the Airbenders! Is this the cause of the pollution Aang finds there, or is a more mysterious menace afoot? [via Dark Horse]
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