Doubled Jeopardy

With the coppers wide-eyed and aghast,
This proper doc's ride ends at last
As his head rearranges,
And from Edward he changes,
He says, "Swapping with Hyde was a blast!"

Dr. Jekyll (Fredric March), at rest in his lab in Dr. Jekyll and Mr. Hyde (1931). Title by double standard-bearer Donald B. Benson.