First of all let me admit that I don’t know enough about the genre of children’s books to make my review and opinions accurate. However, it would be good to know the age group at which your work is directed as this will surely make a difference to tone, content and plot.

I really like the adventure drive behind your story concept, however, I don’t feel as if the narrative is engaging enough to captivate the reader and draw them into the adventure your protagonist is embarking on. Theoretically, a small boy on an adventure in a dark cave should be exciting, but there needs to be more pace and telling details to bring the scenes, motives and actions to life. Ways of accomplishing this might be just to shave out a lot of dilly-dallying detail and hone in on the most important bits: take out some of the references to the Swallows & Amazons cast (it could be confusing to the reader who hasn’t reader classic), don’t stall for so long when he is deciding whether to go back inside through the front or back door of his house (yawn) and when he enters the cave, relay only the most adrenaline-provoking part of his journey – twice he says to himself that he hasn’t broken anything, but what we really want is to smell and feel his surroundings and his fear – unless of course you intend him to be very logical and fearless, but surely a small boy tunnelling into the pitch black on his own would be scared?

Currently, a lot of the narrative relies on Tristan’s internal thought process (about his mum, his adventure etc), but the pace might clip along a bit better if you dropped some of the mulling and brought the plot to life with more observation of his surroundings. I’ll go back to the bit when he is deciding whether to use the front or back door of his house. The doorbell goes – who is it – can he see them? He hears his mum’s voice – what does she sound like? Who is she speaking to and what do they sound like? What is the inside of the house like? Tiny details will make your writing much more visual.

I like the introduction of Sebastian and think this will work to create a more dynamic plot – although will the subtleties of his Aspergers be lost on the younger reader? Although you make a point of him being ‘weird’, it might be better to point out what it is that strikes Tristan about this boy he has just met – why does he like Sebastian even though he finds him strange? What makes him weird?

Overall I think you have the workings of a promising idea – it just needs a little tightening to get it moving. And (like the rest of us), it needs the grammar tidied and a captivating title! Good luck.