**Core Concept**
Non-contrast computed tomography (CT) is the best investigation for diagnosing ureteric stones due to its high sensitivity and specificity. It provides detailed images of the urinary tract, allowing for accurate localization of stones and assessment of potential complications.

**Why the Correct Answer is Right**
Non-contrast CT scans are particularly effective for detecting ureteric stones because they do not require the use of intravenous contrast agents, which can obscure stone detection. The high-resolution images obtained from CT scans enable clinicians to identify stones as small as 1-2 mm in size, facilitating early intervention and minimizing the risk of complications. The absence of contrast also reduces the risk of allergic reactions and nephrotoxicity.

**Why Each Wrong Option is Incorrect**
**Option A:** Ultrasound is not the best investigation for ureteric stones due to its limited ability to visualize the ureters and potential for poor image quality. While ultrasound can detect some stones, it is often not sensitive enough for accurate diagnosis.

**Option B:** Plain radiographs (X-rays) are not effective for detecting ureteric stones, especially small ones, as they may not be visible on a standard X-ray. Additionally, X-rays expose patients to radiation, which is a concern for patients with multiple stone episodes.

**Option C:** Intravenous urography (IVU) involves the use of contrast agents, which can obscure stone detection and increase the risk of nephrotoxicity. While IVU can provide detailed images of the urinary tract, it is not the preferred initial investigation for ureteric stones.

**Clinical Pearl / High-Yield Fact**
Non-contrast CT scans are the preferred initial investigation for suspected ureteric stones due to their high sensitivity and specificity, allowing for accurate diagnosis and timely management.

**Correct Answer:** C. Intravenous urography