'How dared you?' versus 'How dare you?'

This seems to be a quote from Robert Gilbraith's The Cuckoo's Calling.

In the original, the 'dared's are italicised for emphasis. They refer to an event in the past. The question is repeated in shorter form immediately after, for emphasis.

If you flip the question to a statement, you'll see that, although unconventional, it's a reasonable and grammatical construction:

You dared go and see her without me.

So, I can't see a problem with it in context. You could argue it adds to the drama.

"dare" can be used as a modal: "How dare you go there alone?" (compare with "how can you go there alone?") - "go" is the main verb

"How dared you go and see her without me?" is simply the simple past version (compare with "how could you go and see her without me?")