I tried this plugin and found that it didn't suit our needs, so I used MyCalendar instead.
Seems I didn't deactivate the plugin straight away, then during a tidy-up, I deleted the now redundant "Events" category.
This trashed the whole site. i.e. no page would load its content. Just got "Page not found" and a header, something along the lines of "Calendar of Events"
Resolved by deleting the plugin, but caused unwelcome downtime until I realised.