It's 4.30arn on Saturday morning and a tiny ping denoting a new text message on my phone startles me awake.
If you live in London you learn to sleep through ambulance sirens going past your house, but one tiny bleep can summon you from deepest oblivion if it might mean a text from your 18-year-old son among the pilgrims at World Youth Day in Australia. Especially when that son normally never speaks to you.
Only parents of teenage boys know the true meaning of the words "communication breakdown-. Even the most truculent daughters live in a welter of texts, but boys can observe radio silence faithfully for years.
He keeps me on a daily ration of six words — usually "go away and leave me alone". A typical text from my first-born once read simply: "Mum stop getting involved".
"Probably asking for more money," I mutter grumpily, reaching for the phone. I am wrong: "See it all on TV Channel 769," he has written.
He wants us to watch the broadcast from Australia on EWTN! The first-born is huddled in his sleeping bag on Shandwick Racecourse, and he wants to share the moment with us — his despised, horribly uncool parents!
Either that, or some supernatural force which makes teenage boys talk to their parents has stolen his phone and is texting us on his behalf...
Ever since his father conceived the mad plan of grabbing a last-minute place on the holiest of youth events for the least holy 18-year-61d in the parish I continually expected him to back out. The signs weren't good: he boycotted the pre-pilgrimage prayer meeting and Sunday Mass, on the grounds that "he had to spend two weeks praying in July, and that's enough".
I shoved him through Heathrow security with a hasty hug two hours too early, fearing he'd do a runner at the last minute. When the first text message arrived from him claiming to be in Australia, I suspected it really came from a pub in Bromley. Then our parish priest — who has for years urged me to have faith in my boy — spotted a photo of him on the diocesan website: genuine photographic evidence that far from being in a pub in Bromley, he was in fact enjoying himself in a pub in Sydney.
An e-mail arrived: again uncharacteristically cheerful, describing the opening Mass as "fun-. Mass? Fun? This is getting weird. The "Talking to your Parents is OK" spirit hasn't just nicked his phone. Now its hacked into his email account.
The last text was so downright nice that the boy's younger brother thoughtfully suggested: "It might be like, you know, that French guy with the long nose."
"Cyrano de Bergerac?"
"Yeah. Someone's writing his texts for him.
Now it's 9.30 on Saturday morning, EWTN have finally got around to showing us Sydney, and the Pope speaks of the power of the spirit of love. I cannot picture my scowling, computer-, televisionand sofa-bound young man taking in a single word or swaying sweetly to "Receive the Power".
But at the unforgettable sight of the Pope outlined in brilliant light, waving to a sea of candles held by half a million believing Christians, I realise how wrong I have been. What right had I to think I knew my son better than God himself?
How dared I doubt that he could respond to this amazing experience? The lack of faith and excess of cynicism that I should be worried about are not my son's, but my own.
Young people are more open to the Holy Spirit than we ever give them credit for. The Pope believes in them: so should we.
Sarah Johnson is the author of The Christian Parents Toolkit (Continuum. £10.99)