was Frenchy in for something else and the Doc amputated his perfectly good arm by mistake??

No

Ghost - can we give on this one?
I just want to know the answer...!!

The two guys were on a cruise ship together. The ship sank, and our two protagonists shared a lifeboat (alone). They were separated from the rest of the shipwrecked, and at some point in time, their food was all used up. So, just at the brink of starving, they chose to amputate a limb and eat that...

The guy from London, being a M.D., had good arguments to be the second in line when it came to giving up limbs - after all, HE was the one that could do an amputation by profession. So they struck a deal: The Frenchman would be first to have a limb amputated, but the Englishman would have the same limb amputated if they returned home.

When they were halfway done with eating the arm, they were spotted and rescued, so Mr. Englishman had to have his arm amputated after the safe return home... to prove he did it, he was supposed to send the amputated arm to Paris...

As I said, the corpse in the river Seine had nothing at all to do with the story...

OK, seriously?? We were supposed to figure That story out?!?! I wasn't even close to getting that one right!

You want an easy one? I can do that...

Sure! I like easy!

Bloody ell.......I'd a never figgered that out!!!!

Yeah, I know...like That was my next guess