**Core Concept**
Fever, clubbing, and Osler's nodes are classic clinical manifestations of a systemic disease. Endocarditis, a condition characterized by infection of the heart valves, can present with these symptoms due to the body's immune response and the septic emboli that form.

**Why the Correct Answer is Right**
The combination of fever, clubbing, and Osler's nodes is highly suggestive of acute bacterial endocarditis (ABE). Osler's nodes are painful, indurated lesions that typically occur on the skin of the hands and feet. They are caused by the deposition of immune complexes and the activation of the coagulation cascade, leading to microvascular thrombosis. Clubbing, characterized by an enlargement of the distal phalanges, is also a result of the body's response to the infection. The fever is a systemic manifestation of the infection and the body's inflammatory response. The correct answer is Endocarditis.

**Why Each Wrong Option is Incorrect**
* **Option A:** Sepsis is a systemic inflammatory response to infection, but it does not typically present with Osler's nodes or clubbing.
* **Option B:** Chronic kidney disease can present with fever, but it is not characteristically associated with Osler's nodes or clubbing.
* **Option D:** Rheumatoid arthritis can cause clubbing, but it is not typically associated with Osler's nodes or fever due to a systemic infection.

**Clinical Pearl / High-Yield Fact**
The presence of a new heart murmur in a patient with fever, clubbing, and Osler's nodes is highly suggestive of acute bacterial endocarditis.

**Correct Answer:** C. Endocarditis.