The sky's on the edge of blue to grey as we turn off the road into the tunnel of trees. The back end of a long day, we're almost home.
For a change, I'm driving whilst Tam sits in the passenger seat, flushed with the glow of a 3.35 London Marathon, but yet to feel the gnawing verocity of its after-effects.
She's telling me of a text message she received as she waited that morning at the start area.
She pulls out her phone, scrolls through, finds it and reads it out.
'Hi Tammy.
Just wanted to wish you good luck - I'll be thinking of you - and to thank you so much for your love, support and kind words you have for Robbie. It means everything to me. It would to Robbie as well. I'm sure he'll be there with you the whole way. Look after him for me please. Thank you again, Tammy.
Take care, lots of love, Robbie's mum.'
She couldn't help crying, she tells me.
I look away from the road for a moment, turn my head to the left, tears in my eyes, and look at her.
She's crying now, too.
Over recent years, I've become a cynic when it's come to big city marathons. I've moaned about the extortionate entry fees and the virtual impossibility of securing a place through a ballot that's subscribed to its limit within a few hours. I've ranted about the 'charity hi-jacking' of mass participation road races, the obscene number of places they get allocated at the expense of the club runner, and the culture which looks down upon any athlete who wishes to participate in a race for the singular beauty of the challenge, rather than 'doing it for charity'. And I, too, have looked down on the runners who gravitate towards such events. Why run 26 and a bit miles on faceless tarmac in a cattle-crowd of thousands of people, when you could be alone, a part of nature, running wild?
I'm good at voicing my opinions, I guess, and even better when that opinion rails against the widely held view. And I've been pretty decent at slagging off big city marathons to anyone who knows me.
But stood on Tower Bridge at 10am on a London Marathon morning, something changed. I saw something clearly for the first time, and I realised something important too.
I realised I'd been wrong all along.
It's the mark of a man's life that the world around them is changed by their presence. To change the world around them when they're no longer here is, perhaps, an even greater sign that the life they lived was important.
It's a few months since Robbie left us. I can't count myself as privileged to have been a good friend of his. Robbie, to me, was just one of the dads at the school gates. He was the good looking postie with the cool tatts, the flip-flops and the smile who'd wave as he passed you in his red van. He was the running buddy who'd occasionally pop along on a training night or who you'd see at a Wolds Dash race, chat to for five or ten minutes, before getting on with your warm-up or cool down. He was the sort of guy who'd stir latent, stupid, school-kid-jealous thoughts - the kind you used to have which whispered inside your head, 'I wish I could be more like him.'
I wish Robbie had stayed around. For my own personal reasons - I would have loved to get to know him better - but also for reasons infinitely more important. I wish Robbie could have been there for his mum as she grew old, could have been around for his daughter as she grew up. I wish he could have partied with his friends on a lifetime of Saturday nights, and I wish he could have felt the immense pride of walking his sister down the aisle as she wed.
But Robbie's gone.
It's strange, therefore - so sad, but comforting too, that, even as someone who knew him only briefly, I've seen him so many times as the world has turned through autumn, winter, spring.
I've seen Robbie in the mornings as the Royal Mail van pulls up outside the office door. I've seen Robbie on the drive home, walking past the bakery, cap on head, arm wrapped in clingfilm, protecting fresh artwork. I've seen him on every run along the bottom path through Hubbard's Hills, running towards me, blue tee-shirt, shorts and a headband, his i-pod strapped to his arm. I've seen him in the look on Tammy's face as she's pulled on her running gear, ready to brave the foul weather on another long and lonely Sunday run. I've seen him, too, in Rhea's eyes as the band his mates played in reformed for her wedding day to play a song he loved for the married couple's first dance.
Team Running For Robbie was put together in July last year. Members of his family and a host of friends have competed in various races and long distance challenges to ensure Robbie's life is never forgotten, and to raise funds for PAPYRUS - a charity that works to help prevent suicide in young people. Tammy has told me countless times over recent months how proud she feels when she pulls on the PAPYRUS vest with Robbie's picture on the back. She's mentioned something else a few times too. When she's tired, going through a bad spell in a race or struggling to reach the finish, she'll have a little word with Robbie. She'll remind herself why she's doing what she's doing, and she'll imagine just one person in the crowd who's watching her - a young man or a young woman, just like Robbie. Just one person who can't see a way forward, but might see Robbie's picture, call up the Hopeline number above it, and realise that, however dark things seem, there's always someone, somewhere, looking out for you.
The crowds are dense, excited and noisy on Tower Bridge. I'm waiting with my great friends from Mablethorpe Running Club. I'm looking for the sight of Tammy, heading for the half-way point of the marathon. I'm thinking of Robbie.
I'm with friends, good people who look out for me, people I love. I look over the bridge and take in the people on the opposite side of the road. All are in groups. There's laughter, shouts of encouragement, enthusiastic cheers. It's almost overwhelming. In the wake of the sickening events of the Boston Marathon, people have come together - to celebrate the spirit that guides and binds us, to remember, to be there for each other, to watch over their fellow men.
Tam comes and goes with a pose for the camera, a mad wave and a grin as big as a rainbow. And before long, the joggers and the walkers start to stream past. 'Charity runners'. Never had any time for them. Until now.
I think of the passion Tam has invested in her chosen charity over recent months. A charity that means something so important to her. A passion stoked by a belief that by running 26.2 miles, she can make a difference.
All around me, there are thousands of people just like Tammy. They're doing this because they care. Because they want to make the world just a little bit better. Because they're human, and humans look after each other.
And I'm seeing things differently. The over-weight woman with the red face in the Children with Cancer UK vest is a mother who lost her daughter too early to the cruel disease. The young lad walking with a limp in the Heart UK vest is a son who watched his dad collapse and die. The girl with the pony tail who looks nothing like a runner in that Help For Heroes vest? Her brother never returned from Afghanistan.
My imagination. But the truth. Ordinary people don't just pick a charity out of a hat. They choose one because it means everything to them. Then they dedicate themselves to the hardest physical challenge they've ever attempted in their lives. They might run. They might jog, or they might walk. And it really doesn't matter how they get round, how quick they finish. Because these people - well, these people are amazing.
There's hardly light left as I'm jogging by the drain. A little leg-stretcher after getting home from the marathon.
Robbie's mum's text in my mind.
The only sound is a whisper in the ether.
'We're human, and humans look after each other.'
I think of Whirlwind and Lightning's big squeezes when we'd arrived home. I think of Tammy, my family, my friends - the people I'd do anything for, and who would drop everything to help me.
'We're human, and humans look after each other.'
I think of the charities and organisations I've seen today that work tirelessly to give help to people who need it. Of the people who've succeeded in a challenge they'd previously never dare dream of, to raise money for these charities.
'We're human, and humans look after each other.'
Then I think of the ones who've left us, but who's presence is still felt so strongly in our everyday lives. Those who watch over us.
Leaning against the gate, back at home, the sky is dark. My eyes are drawn to the red lights of the distant Belmont transmitter, but I'm not really looking. Instead, I'm seeing Robbie running into the finish in his last race. Appearing over the wooden bridge and sprinting down Hubbard's Hills bottom path, he looks hot and tired. He's a right to be - after all, he's completed his first London Marathon today, watching over Tammy for every step of that 26 miles.
As he comes nearer, his smile is unforgettable. I remember the words of the text Tammy read to me an hour ago, and I smile too.
'Look after him for me please.' You did that Tammy. Robbie's mum would be proud.
* * *
The website for PAPYRUS is here.
Tammy's Running For Robbie justgiving page is here.
Robbie's good friend, Andrew Tomlin is Running For Robbie in the Manchester Marathon on Sunday 28th April. His justgiving page is here.