Writing a review where you can't mention anything at all about what happened in the show is pretty challenging.
But because Derren asked so nicely at the start, I'll have to give it a go!
You've probably seen what Derren does on television - a mix of hypnosis, illusion, suggestion and mental gymnastics, so I knew to expect some or all of that in his live show.
I've been a fan of his for a few years and the first thing I remember seeing him do on television was convincing a cashier at the races that he'd won and being handed a wad of money, despite his betting slip showing otherwise.
Over the years participants in his stunts have found themselves in situations I'd find absolutely terrifying, most recently with Pushed to The Edge, where ordinary people started the evening at what they thought was a work event, but ended up shoving a man off a roof by the end of the night.
It's fascinating to watch how easily some of us can be manipulated - including people sitting in the audience, arms crossed, clearly believing he could never do it to them.
I believe hypnosis works better the more suggestible you are; if you think you're under a magic spell, and also because Derren is quite an authoritative figure.
But he doesn't even have to hypnotise anyone to get them to do something, and I find that the most intriguing part of his act - how he can predict and influence what people do, seemingly from knowing nothing about them at all
The one part of the show I CAN talk about is when Derren asks his Twitter followers to reply to a picture of the audience with a single word - and you can guess that forms part of a clever trick later on.
Here's Derren's tweet from the night we went to the show.
One person correctly guessed 'spatula' which Derren had predicted would be one of the replies - and once it was revealed, Twitter users were asking why he'd picked that word, to which he said: "I have no idea - I normally say sausage!"
I have absolutely no idea how Derren does any of this, but I do know he's a bit of a philosopher - and maybe his assertion that we're not as unique as we'd like to think we are is how he seems to be reading our minds and predicting what we're going to do.
It's no surprise that Derren's show was a sell out every night at the Grand - even though he tells you he has no magic powers, you seem to be watching magic happen before your eyes.
And don't worry if you think you're going to get pulled out onto the stage - that only happens if you want it to...
Derren's opening a rollercoaster at Thorpe Park - here's what he's got planned for those brave enough to take a ride!