This is a great little story, but it needs some tightening up. Here are a few suggestions; and remember this is just my opinion. Take what you can use and leave the rest.
Walking along the water's edge,Tom often snickered to himself, a habit he'd started after the incident.
I had to read this twice in order to understand that he was walking along the water's edge right now. "Tom
often snickered to himself" makes it sound like it's in the past. Try this:
Tom snickered to himself as he walked along the water's edge, a habit he'd fallen into after the incident.As lightening it struck him, the boy was drowning.
I see two things wrong with this: It's a cliche and it's not very clear. If you want to keep the reference to lightening, try this:
Then lightening struck. The boy was drowning. The reader will understand it refers to a sudden realization.
People said it was the reason why so many had lost their lives in the lake over the years. It'd happened to a boy in Tom's class on a Christmas morning long ago.He had strapped on his new skates, and then went for a spin on the deeply frozen lake. By evening, they found him close to shore under the ice. Everyone knew the ice was thin over the warm springs; they said he’d misjudged the edge.
The image of someone lying in their coffin is excellent, adds to the tension and creates a sense of urgency. But the backstory is a diversion from the tension that has been building until now and, therefore, only proves to be frustrating. I would find a way to introduce the image in one or two lines and cut out the rest.
Some who had drowned had disappeared without a trace, so to speak.
What does it mean--so to speak? Either they disappeared or not. Also, it sounds like the author is speaking to the reader. I'm not an author intrusion Nazi. Sometimes those intimacies add something to the story that makes it come alive, but I just don't think it belongs in this story, and certainly not at this point, while our hearts are racing.
In a home, maybe Frankie's, someone Some of the townspeople would be missing at the dinner table tonight while they began to drag the lake.
"In a home" makes it sound like just one person will be dragging the lake; and "maybe Frankie's" makes it sound like his family will all sit down to dinner as usual, except for the one who's worried enough to go out an search.
He came to his senses after what seemed a long time, though it was seconds.
This is written from Tom's perspective, so there's no way he would know that only seconds had passed. He either experienced it as a long time or not.
but he knew he needed to get back to solid ground to get away.
The island isn't solid ground? Then what is it?
I would cut out the last graph and leave it at "This hadn't been his day to die after all." That would allow the tension to linger a bit after the conflict has been resolved.
That's all I have. Thanks for sharing this. I enjoyed it.