Sorry .. there's a reason I don't recap - I suck at it. 
The clip you posted is of the last part of the song when PHJB took over.  Before that Warren and Grace shared the vocals - trading off the verses - there's more of Warren's guitar work too.  Grace can sing anything, as can Warren, and I love both of them whatever they do, but I have a soft spot for the blues and they can hold their own with the best of them - and did.   Would love to have their performance of  “St. James Infirmary" tucked away in the vault.