Big Fail – When site is accessed "IS SET" is displayed

After attempting to activate a plugin, the page didnt reload correctly and now when attempting to access the site, it displays “IS SET” in plain text…

Here’s a link to the site: https://bagging-scotland.com/mybag/

Cant access the site in anyway and am not confident (at all!) with database adjustments, but willing to hear any suggestions as this is a pretty major disaster!