Hiya Dave and welcome to Aquariumadvice.
Urk. Not sure about ich if theres only one spot. Does it look more like a pimple or a grain of salt? My off the cuff guess is columnaris. The thin white film (and white pimples) are signs. It can also kill very quickly. But before I say for sure, what are your water parameters (ammonia/nitrite/nitrates)? Ammonia can also cause skin issues as well as kill fish. Do check them and let us know. In the meantime, also check out this link about columnaris: http://www.aquamaniacs.net/flex.html
I'm guessing the fish weren't quarantined? Just for future reference, perchance they weren't, grab a cheap 10g and a heater n filter; it will save you heartache in the future if you QT
new fish for at least 2 weeks.
Aww, and I'm sorry about the plec
aka Cycling Guru and the Ich Slayer
*glares at Terry and QTOFFER*
Card carrying member of FTAS & GCAS.