Nessus

I just ran my first one-shot scenario - Genius Loci from Doors to Darkness. My player's first instincts were not to research the asylum or go to try and see Larry but to infiltrate the asylum as patients and staff. This threw me for a loop I don't mind telling you. I'm interested to know how other keepers would have handled it? Luckily ( for me ) the player trying to get in as a patient halfway through meeting Dr. Berger realized that he had given his character's real name and that both of the letters from Larry had been addressed to him so he just came out and accused Berger before I had to go off-book and have the players committed. I know that this should be no sweat for an experienced GM and I might just have to take my knocks until I get to that point but does anyone have tips for brain lock when your players do something totally out of left field? I really don't want to be a GM that railroads my players but I came very close to it ( to the point where they asked me if there were secret tunnels or storm drains in the maps of the asylum later and I absent mindedly just said no instead of working with it ) I'm also having some difficulty with expectations of what players can do in classic cthulhu. I'm happy to pulp it up if that's how the party tends to go but in my mind having infiltrating the asylum as your very first reaction to the letter seemed unrealistic, especially without at least casing the place for a week or two first or checking if they were hiring staff, admission policies etc. At the same time I want to own this as a gm, not blame players. Any idea is a good idea if it's fun for the whole table.