Slippery when wet...

I'm going to be quick with this post, because I'm writing it via mobile phone technology.

I'm sitting on in the garden of a house in Richmond, situated on the river Thames.
Deadfast is ten feet away, on the steps that lead down to the river, and he is calling me over.

We've been in Persuasive Pete's house for two days, and... I am about to get into a two-man submarine.

HELP!