The lengths that Mary and Francis are willing to go to save each others lives is just on such an intense level. Francis would rather risk Mary hating him forever then let her get on that boat and take the chance of her dying.
The thought of them losing each other makes them go bat shit crazy and they come up with the craziest solutions. This ep was so fucking good, though.
Francis just did EXACTLY what Mary did in 1x09. The only difference is Francis had proof that there was a plot to kill her.