Pass Content to Template

First of all, thanks for the plugin! I managed to get all set up very easily. My plugin is firing out messages using the Mandrill API and I’ve even got it selectively using different templates for different purposes using the wpMandrill::mail function. However – and admittedly I am coming to this with no prior experience of Mandrill – how do I pass the $content into my template? I’m looking at merge tags but drawing a blank. Could I get a nudge in the right direction please?

PS: A little help with attaching some metadata would also be appreciated as I need to pass an ID for the link destination.

Thanks again.