How do I reinstall an application that appeared not to have installed?

Yesterday I bought an application on the App Store - I paid and the install button did its dance onto the Launchpad and I saw the download progress etc. When all was completed I went to my Applications folder and there was no trace of the application (Pitchuresque by Aquilia).

I checked my purchases in the App Store - and there it is right at the top saying "Installed". So now I'm stuffed as it seems I cannot either attempt to buy it again or reinstall it. I have no idea what went wrong but it certainly did go badly down the tubes on this occasion.

Can anyone advise me on who I need to contact to try to sort this out please?

Thanks.