There was a brush of carpet as William’s bedroom door opened and I hurriedly put the handbag back on the hall table, stepping back into the shadows of the lounge. I could just see their feet crossing the landing as Mel shepherded William in front of her to the bathroom. A click-clack as the bathroom light cord was pulled, a slab of light spilling out onto the landing. I hesitated – just for a second – feeling my heart thudding in my chest. My wife had already betrayed me, I knew that, but she had asked for my forgiveness. She had lied, and I had found her out. So what was this?

It is better to know.

I stepped back out into the hall and went back into her handbag, reaching up and through the lining until my fingers touched smooth hard plastic. I grabbed it and pulled it out.

It was a compact Samsung mobile phone – black, no case, new-looking.

Mel had owned an iPhone for as long as Apple had made them, she wouldn’t use anything else.

I had never seen this Samsung before.

It only had one button that I could see. The phone’s lock screen came to life, a keypad and prompt asking me for a four-digit pin.

Four digits. What would she use? Presumably I had three chances to get it right before the phone locked me out.

Her birthday? 15 September. 1509.

The digits of the keypad shook. No good. The sound of Mel’s voice reached me from upstairs, calm but firm, her you-will-clean-your-teeth voice. It would be maybe sixty seconds before they were done in the bathroom.

When was Ben’s birthday? I didn’t know. Shit. Sometime in January.

What else would she use? We used our house number as the parental lock on the TV to make sure William didn’t stumble across Game of Thrones on catch-up.

4343.

The keypad numbers shook again. Wrong. A bead of cold sweat traced a line down my ribcage.

Last chance before the phone locked. I tried the only other combination I could think of: William’s birthday.

1406.

The phone unlocked to reveal a screen full of apps. His birthday. Of course.

I was in.

Work fast.

It was on silent mode, which made sense. I hit the text messages icon.

The screen showed: empty

She must delete as she goes along, I thought. Smart.

I heard the toilet flush from the bathroom upstairs. Concentrate. Call history: see what calls had been made and received from this handset in the last few days.

The screen showed: empty

No calls in memory. No texts either. I found this bloody phone, figured out the passcode, this can’t be a busted flush. It can’t be. There had to be something, somehow, that I could learn from it.