Take an old friendship, an even older boat, and a dream of sailing to St Petersburg . . .
Add the fact that Bob can't sail and won't listen, include a smattering of North-Eastern European countries whose sole purple is to corrupt middle-aged men - and chuck in a few rocks.
What you get is a bravura tale of the cowardly all at sea; a ripping yarn of a relationship running aground; and the distinct possibility that neither Bob nor Griff will ever manage to plot a course back to normality . . .