It sounds like you read the first four! The one with the Doctor was, IIRC, the one with the computer planet. (The one with the whales is also my favorite though. <3) There was a very long gap between the one in Ireland and the next one, which i I file as "the super-sad one"; I think a lot of people lost track there. You don't meet Sker'ret until rather later, it's true, but he is great.

But it's mostly that I was mixing canons with great abandon in my post. ^_^