The Drowning ending explained: How did Jodie's son Tom go missing?

Episode four began with a flashback to the day when Jodie's son Tom went missing, with shots of divers looking at the bottom of the lake.

In the present-day, Daniel's father Mark (Rupert Penry-Jones) is seen in handcuffs, following The Drowning episode three's revelation that Daniel is a genetic match with Jodie - meaning that he is her son, Tom, and not Mark's child.

We see an awkward family reunion as Jodie introduces Daniel to his long-lost family, including her increasingly shifty and narcissistic brother, lawyer Jason (who was always a little strange, as discussed in our The Drowning review).

However, it's clear that something isn't adding up, with increased confusion about Daniel's identity.

In one scene, Jodie starts screaming when Daniel bites into a prawn sandwich, recalling that toddler Tom had a severe shellfish allergy - but a perplexed Daniel admits that he'd always eaten shellfish as long as he can remember.

Jodie's ex-husband, Ben, and his new partner Kate then rock up to Jason's chambers, where they suggest that they have reservations about Daniel's parentage, and that they should get another DNA test done - and Jason hits the roof, for no clear reason.

Of course, Jodie had already taken an at-home DNA test during episode three (prior to the police DNA test). Halfway through the finale she gets the results back: negative. According to this first DNA test, she and Daniel aren't a match, meaning he couldn't possibly be Tom - so which test is telling the truth?

Foolishly she informs Jason about the negative DNA test results, and, unbeknownst to her, he kidnaps Daniel and drives to a patch of private land, located - surprise, surprise - by the very same lake where Tom went missing almost a decade ago.

We also learn the real reason why Mark hated talking about his wife, Daniel's mother: she had died by suicide, and Mark was always terrified that Daniel's memories of the tragic event would come flooding back and traumatise him.

In the final minutes of the episode, Jodie and her mother catch up with Jason at the lake, and the truth finally comes out: it was Jason who was inadvertently responsible for Tom's drowning, after taking his eyes off the toddler when he was on the phone.

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Worried that he would be implicated in the death and that his career would be ruined, he never spoke up about the incident, despite knowing the location of Tom's final resting place.

Years later, he'd faked the police DNA test results for Daniel, and was determined that no conflicting test results would ever come out and reveal that Daniel wasn't Tom after all.

Clearly intent on murdering Daniel, Jason chased both the teenager and Jodie into the lake - where he appeared to drown.

At the end of the episode, we saw Jodie finally holding a funeral service for Tom, and it was Daniel who laid the wreath.

Looking for something else to watch? Check out our TV Guide.