The Walker's Guide is brilliant, and I'm not saying this just 'cos Tristan is a mate, it really is.
I've spent years walking, watching the clouds and sky and yet reading this I learnt masses.
The best way of describing this is that Tristan is Sherlock, seeing clues in the natural world that others miss, whether the geometry of rainbows, the shape of leaves, messages sent by butterflies and much much more.
I did wonder if Tristan is indeed Sherlock, who would I be? Watson maybe - or least one of the Watsons? Hopefully not a Lestrade anyhow.
As well as being comprehensive with 850 clues and signs, it is also a fantastic read, slipping down easily. Since reading it I've been listening out for the calls of birds and looking again at the angles tree branches make, seeing the world afresh, and how many books can do that?
Check out this review - in which I leant something else new.
Apparently something we learnt on our trip to the Arctic Circle is now part of the survival guide for Britain's force's air crews.
That's brilliant too.