Howard Confronts Leslie About the Letter, Explained：talk very plainly

I didn't write it. I swear I didn't write it.

Leslie denies the letter flatly and backs it with an oath, the first of several versions she gives Howard.

Then it'll be a forgery.

She argues that if the handwriting matches, the letter must have been faked, trying to keep her denial alive.

It's not dated. It might have been written years ago.

She searches for an innocent explanation, suggesting an old letter rather than one sent the night Hammond died.

I did write that letter, but I was afraid to mention it.

Her admission reverses the denial, and she frames the lie as fear rather than guilt.

I was forced to stick to it.

She says she could not take back her earlier claim of having no contact with Hammond, so she kept repeating it.

Then you'll be called upon to explain why you asked him to come to see you when Robert was away.

Howard shows the real problem: if she invited Hammond, she must account for the visit while her husband was gone.

Leslie, I shall have to talk very plainly to you.

Howard signals that the polite questioning is over and he is about to say what he really thinks.