Now, what you've all been waiting for, a friendly game of tennis! Well, not so friendly. Light is trying to figure out L's true identity while L tries to determine whether Light is Kira (spoiler: he is), and they're each using the match as cover to analyze every word and move the other makes. The match itself is dull - stiffly animated and not trying to be an accurate representation of the real thing - but during the match we get a look inside the competitors' heads as they try to anticipate the next move. They know each other well.
Light's dad, the elder Yagami, is under pressure from his boss, who's under pressure from the media. They argue about stuff, and Yagami assures his boss that L is trustworthy. After their match, L reveals to Light that he suspects him to be Kira, "but only 1%." Then they have tea, and L shows Light the messages Kira made prisoners leave in episode four. Light tells him about the hidden message, which I still think wasn't originally intended to be a plot point, and L reveals... a fourth message!?! Light is shocked, because he knows this last one is fake, but he doesn't show it, correctly guessing that L is trying to goad him into throwing a fit. It's a clever ploy, since Light's ego is his greatest weakness, but he's just a bit too smart to fall for it. Maybe if he hadn't had his guard up already. Light turns the tables on L, accusing him of being Kira, but overplays his hand by asking for proof that he's really L, something L already predicted he'd do. L continues to elevate his personal risk in an attempt to flush Kira out, and is seemingly on the verge of inviting Light to the investigation headquarters when they receive simultaneous phone calls! Light's dad just had a heart attack!
It's not Kira, of course, and it's not fatal. He was just stressed out from the case. While they're all together at the hospital, Yagami confirms that L is indeed L, so Light gets what he wanted... or does he? L explains why he suspects Light (the Ray Penbar disaster), and Light says he'll help with the investigation, promising his father that he'll "send Kira to his execution" himself. Heh. Light's little speech has Yagami convinced that he can't be Kira; even L thinks he's sincere. Yagami reminds us why he's the one true hero in the series, explaining to Light that while he believes Kira is evil, more than that he believes the power to kill is evil, and he pities whoever was burdened with such a power. His words cut straight to the heart of the series. Had Light not found the note, he'd have likely become a great detective. Maybe he'd even develop the capacity for love. As it is, he's doomed.
Light is torn up inside. He feels horrible that anyone could think he might be the vicious mass murderer Kira. Like, totally! He asks L if there's anything he can do to prove his innocence, going so far as offering to be locked in a cell for a month, his every move observed. L declines. Alone with Ryuk, Light shows his true self, barely able to contain maniacal laughter as he talks about how great it was to find the note and how thrilled he is by the prospect of the utopia he intends to build atop a mountain of corpses. We shift locales to a scummy news network willing to run any story - the more sensational, the better! They're out of ideas, but don't despair, here's a package from Kira himself! Cassette tapes and a letter, proof of his Kiraness and a message to the world.