(I've actually been fanwanking a lot of the harder-to-believe stuff in the series, like Helen's claim that she removed and froze Ashley's embryo ... in 1880 ... the ONLY thing I can bring myself to believe here is that she simply doesn't want to admit to Will that she had sex with Druitt as recently as 1985 or so, so she came up with this lame story that he believes because he's, well, Will.)

If your suspension of disbelief breaks there, this really may not be the show for you -- you really have to buy into steampunk-y Victorian mad science being possible in the show's universe.