Probably The London Eye Mystery (2007) by Siobhan Dowd, who passed away the same year.
From Goodreads:
Monday, 24 May, 11.32 a.m. Ted and Kat watch their cousin Salim get on board the London Eye. He turns and waves and the pod rises from the ground.
Monday, 24 May, 12.02 p.m. The pod lands and the doors open. People exit in all shapes and sizes – but where is Salim?
Ted and his older sister Kat become sleuthing partners since the police are having no luck. Despite their prickly relationship, they overcome their differences to follow a trail of clues across London in a desperate bid to find their cousin. And ultimately it comes down to Ted, whose brain runs on its own unique operating system, to find the key to the mystery.
Google Books offers the following quote about mosher and being cool:
'Salim's a mosher, I said.
'A mosher?'
"It's northern for "casual, cool dude", I said.
Found with the Google query book mind "wired differently" "mosher" which returned
this page, which is taken down, but the Google preview read:
“The ABC's of Diversity”
A Selective Bibliography of Multicultural Books for Students in Grades 6-12 ... the two siblings must work together-Ted with his brain that is "wired differently".
