There are a lot of "suspension of disbelief" moments in Five-O. The entire episode of "Welcome To Our Branch Office", was especially hard to swallow, but I enjoyed it because it was unique and a fun departure from the usual police procedural type of stuff.

I agree with Mike about "The Late John Louisiana". I didn't find that relationship too hard to swallow, and in fact that was one of the more believable couples depicted in the series.

Speaking of believable couples, I remember when I saw "Yesterday Died and Tomorrow Won't Be Born", I was impressed by the chemistry between the villain and his wife. It turned out they were a real-life married couple, so their genuine feelings came out on camera. They weren't a young or attractive couple, but I thought to myself, "Wow, they did a good job casting this one", and then it turned out they were really married.