Node/Express/Jade passing username back to view

This is my first project with all these technologies, I typically do Angular, but I am working for a charity ( and keen to learn node ). This is day three.

When a login fails, I do this:

var userId = req.body.email;
res.locals.userId = userId;

This is supposed to store the value so it doesn't need to be reentered. If login fails, it does this:

return next('Login failed. Please enter your details and try again.');

Then in my Jade template:

    if(locals.userId)
        p Welcome to #{userId}
    else
        p Welcome

The actual template has code to try to do what I want:

    input(type='text', name='email', id="inputEmail", placeholder="Email", value="#{body.email || ''}")

But this does not work.

So, I THINK this means my setting a value in the result is lost when I call 'next', but, because it's also passing in this error object to show on the screen, I'm not sure how I would go about making sure this error shows AND make the value pass through . Right now, my text just says 'welcome' and never 'welcome to xx', this is test code, I'm just proving the value is not being passed through.

My question is, what's the correct way to pass the value through to my template, and ALSO trigger the error message that is being shown.

The code, when I step in to it, goes deep in to Express and checks for errors there.