段五郎接到了研究所所长小岛博士的紧急电话，告知自己收到了一条恐吓电话，要求交出一份绝密文件，否则将面临生命危险。小岛博士无计可施，只好求助于段五郎，请他在晚上8点准时来到他的家中，与他详细讨论这次事件。

当晚8时，段五郎按响了门铃，但没有听到回应。他注意到房间内灯光依旧亮着，便轻轻推开门，只见小岛博士昏倒在地旁边，有一块散发着药味的手帕躺在沙发下。segment five's eyes widened as he saw the handkerchief and quickly rushed to help Dr. Isola, who was still unconscious.

Dr. Isola slowly came to, his face pale and sweaty, clutching at his clothes pockets in panic. "It's gone! The secret file has been stolen!" he exclaimed. Segment Five asked if it was a robbery or an assassination attempt, but Dr. Isola shook his head weakly.

"I-I don't know... I heard the doorbell ring while I was watching TV and eating an apple," Dr. Isola stammered between gasps for breath. "When I opened the door, two men with guns forced me into my living room."

Segment Five listened intently as Dr. Isola continued to recount events: how they threatened him with violence unless he handed over the files; how they used a handkerchief to gag him; and how they eventually fled without taking anything else from the house.

As Segment Five finished listening, he picked up an apple lying on the floor near where Dr.Isola had claimed it fell during his attack—half-eaten but still crisp white skin intact.

"Doctor," Segment Five said sternly yet calmly, "it seems you were playing a trick on us." He paused before continuing: "You sold that file yourself."

The revelation hit like thunderstorm in small town - all because of one single detail: that unblemished apple skin should have turned brown by now due to oxidation if truly 30 minutes had passed since being bitten into by Small Island Doctor while under duress

How did segment five expose doctor isola's deceit? It turns out that there is this thing called chlorogenic acid within apples' cells which prevents them from turning brown when exposed air until cell membranes are ruptured or damaged through bite or cut; so even though dr.isola tried hard enough make people believe those robbers took away secret documents after assaulting him ,the truth remained hidden behind one simple fact about apple skins

In other words what happened here can be explained by science alone —apple skins turn brown when exposed air because of reaction between oxygen & chlorogenic acid present in their cells .So why didn’t this happen yet? Because these cells weren’t broken yet .But then why wasn’t it broken after 30 minutes? That’s exactly question we need answer

And thus segment five solved mystery with no more than logic & observation —he found half eaten apple on floor right next door where dr.isoal said it fell down during assault ;but its skin wasn’t turned yellowish-brown like normal would’ve been after some time ,suggesting something fishy going on here

After realizing truth segment five confronted dr.isoal saying “you are not victim ,you are culprit”-and finally got proof needed prove guilt beyond reasonable doubt

And guess what ?Dr.isoal couldn't deny anymore -his own greed led him betray trust of others

Now let’s find out who really stole document & solve case once for good