They ran in eight tries in total with Luke Sayer scoring four and Naro Zimmerman a hat-trick.
Alec Bailey also had a cracking game with the boot, landing seven conversions and a penalty.
Regular coach Mark Stone missed this one as he was needed at a UK wedding.
Keeping in touch via Twitter he would have been delighted to hear that his men had raced into a 10-0 lead after five minutes, concerned that Banks were soon level and horrified to learn his men were 17-14 adrift at the break when Banks were crowing - with good reason given the performance of their fine ball-handlers.
At that stage nobody could have predicted Guernsey would come out on top by such a clear margin had they witnessed the latter stages of the opening half when the excellent Banks back line with Dicky Dawson and Ben de Figuiredo so impressive with ball in hand, were ripping apart the home defence,
Banks, 10-0 down after just five minutes, went into the break 24-17 ahead and having beaten defending champions Les Quennevais the previous weekend, were clearly fancying themselves to win again.
But, remarkably, Guernsey chalked up 40 second half points as they ran up eight tries in total,
Afterwards, Reynolds explained the turnaround. ‘[At half-time] We completely changed the way we were trying to play.
‘We had backs to burn and we were trying to over utilise the forwards a little in the first half, so we said we needed to up the tempo, take quick taps to keep momentum rather than going for set-pieces at penalties and just speed up the game.
‘That’s what we did and it worked – we scored a ton of points in the second half.’