There are two ways you can continue editing on another computer:

1) Publish to the IS Library (requires an IS account).

In the story editor select 'More options...' and then select 'Save this story'.  Click on the 'Publish' button.  Make the story 'private' if you do not want other people to see your work in progress.  Click on the 'Publish Story' button.  This will upload your story to the IS Library.

To retrieve your story on another device, log into IS and select 'Browse the library' from the main menu.  In the Genre list select 'My Published Stories'.  Select the title you want to edit.  Click on the 'Retrieve' button.  This will download the story to your device and allow you to open it in the story editor.

2) Export and Import the raw story data.

In the story editor select 'More options...' and then select 'Save this story'.  Update the story details and click on the 'Export' button.  This will display the raw story data which you can copy and paste to a text editor and then save as a file onto a flash drive, mobile device, etc.

You can import the raw story data by starting Interactive Story and selecting 'Write a story' and then selecting 'Import'.  Paste the raw story data and select 'Import Story'.

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>> Also how do I resume a story I started writing but didn't finish (different untitled story)?

To edit another story, in the story editor select 'More options...' and then select 'Edit another story'.  You can then select a previously saved story or create a new title.

Note: Interactive Story keeps a backup of any changes you make when editing.  It will automatically ask if you wish to continue editing an unsaved story from a previously interrupted session.